Horticulture Lighting

For commercial indoor farming growers

Welcome to this Primer on Horticulture Lighting

“Grow lights either attempt to provide a light spectrum similar to that of the sun, or to provide a spectrum that is more tailored to the needs of the plants being cultivated. Outdoor conditions are mimicked with varying colour, temperatures and spectral outputs from the grow light, as well as varying the intensity of the lamps. Depending on the type of plant being cultivated, the stage of cultivation (e.g. the germination/vegetative phase or the flowering/fruiting phase), and the photoperiod required by the plants, specific ranges of spectrum, luminous efficacy and color temperature are desirable for use with specific plants and time periods.” [source: Wikipedia]

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Horticulture Lighting For Commercial Indoor Farming Growers 17

Controlled Environment Agriculture (CEA)

What is Controlled Environment Agriculture?

Controlled Environment Agriculture (CEA) allows for cultivating plants indoors – mimicking outdoor conditions.

With CEA, variables such as artificial sunlight, atmospheric gases and water and more can be supplied, calibrated and customized for a completely controlled environment that optimizes plant growth.

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Why now is a great time for CEA!

Today, cultivating crops indoors is a growing trend (pun intended). Whether for the luxury of immediate access to fresh produce, for the profitability of year-round crop growth, or for the ability to secure food for the growing population, more people are cultivating crops using non-conventional practices.

Controlled Environment Agriculture has many advantages over outdoor farming, with the most important being able to manage optimal growing conditions throughout the development of a crop.

Traditional Farming Constraints

Traditional farming faces obstacles that make it inefficient, including less land availability, restricted access to water, extreme weather changes, more pests due to global warming, and larger populations, among others.

Even though technologies continue to emerge such as novel agrichemicals that reduce the need for pesticides or fertilizers, more alternative strategies to traditional farming will be required to feed the extra 2 billion people who are expected to inhabit the planet by 2050.

Vertical Farming Opportunities

Vertical farming offers the potential to optimize space and resources indoors by stacking structures that hold growing plants. While several factors play key roles in plant development (pH, humidity, CO2 concentration, etc.), the two most crucial variables to control when growing plants indoors are temperature and light. Providing the right light to plants in enclosed spaces has been particularly challenging. However, CEA technology brings sunshine indoors through lamps that supply artificial sunlight.
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According to this article about indoor farming, under CEA, it is possible to control every aspect of your indoor farm and grow almost anything, regardless of season or your location. As an example, spinach can be grown year-round, whether or not there’s snow outside, in a quarter of the time it would take to grow in a field and half the time it would take in a greenhouse.

CEA Grow Lights

In the past, conventional indoor operations have relied on high-pressure sodium (HPS) lamps to supplement sunlight. However, the lamps’ inefficiencies made them ill-suited to be the single source of illumination because of HPS lamps’ high electric power requirements. There are many other types of lights used to grow indoors, but light-emitting diodes (LEDs) are revolutionizing controlled growth techniques for a number of reasons.

Recent advances in LED lighting have increased their efficiency at converting electricity into light, making lucrative CEA farms now a possibility. LED lights are now powerful and cost-effective enough that they can be the supplemental light source in greenhouses, and the sole sources of light in CEA vertical or indoor farms.

With the advances of adjustable full spectrum LED lamps, exciting plant light recipes can be tailor-made by adjusting settings such as light intensity, duration, wavelength (colour), and illumination schedule.

As a result, the modern farmer can accommodate a unique environment that fits the specific needs of their plant crop species. Moreover, the grower can also modulate light settings (the wavelength range is particularly important) to modify plant physiology to achieve outcomes such as delayed flowering, increased biomass, accelerated photosynthesis, and many other interesting plant signalling responses.

Sustainable Agriculture

CEA farming allows for local production, even in urban areas devoid of farming space. Current research indicates that, after considering transportation costs, the carbon footprint of locally-produced CEA crops is less than that of externally produced crops.
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CEA production will become a significantly greater component of commercial agriculture in the coming decades. Even though outdoor farming currently has a much lower monetary cost than CEA, traditional cultivation methods may not be enough to meet the near-future farming requirements of humanity’s ever-growing population.

Food production must double by 2050 to meet the demand of the world’s growing population and innovative strategies are needed to help combat hunger, which already affects more than 1 billion people in the world, several experts today told the Second Committee (Economic and Financial) during a panel discussion on “New cooperation for global food security”.

Alternative strategies to grow food, such as controlled environment agriculture, are predicted to be essential in properly feeding a thriving planet’s worth of people.

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Retail vs Commercial Grow Lights

One of the biggest differences between retail and commercial lights is their price. While lights found at retail stores can be found for half or even one-tenth of the price of a commercial light, the former are not optimized for indoor commercial farming. Below, we’ll discuss how a commercial lamp is optimized for plant growth.

Conventional indoor retail lightsCommercial lamps for indoor farming
$ Cost less$$        Cost more
X Not optimal for plant growth✔ Optimal for plant growth

Retail Lamps

Typically, lamps sold at retail stores are targeted toward customers in residential or business settings who intend to have their lamps fixed in a room for the comfort of humans— in other words, to please the human eye.

Therefore, you will find specifications related to the environment a retail lamp can create in a room and its effect on the perception of colour and the surrounding space.

The following are examples of technical details often provided in retail lamps’ documentation that pertain more to human comfort than to plant growth:

  • Lumens – Indicates the level of brightness, how much light is given from a source. The more lumens (lm), the brighter the light; the fewer lumens, the dimmer. What’s important about the lumen as a unit is that it is photometric, meaning that it refers to the human-perceived brightness of a source, rather than the absolute optical power or energy a source emits.
  • Colour temperature – Often reported in kelvin (K) units, colour temperature, also known as correlated color temperature, is a value given in the range of ~2,700 K to 3,000 K to indicate yellowish/warm tones, and over ~5,000 K to reference blueish/cool colours. It refers to the equivalent blackbody temperature the light would have; for example, if it were an illuminating star of that temperature.
  • Colour Rendering Index (CRI) – Is a percentage value that indicates the fidelity to which the light reveals the ‘true’ colours of an object, that is, its colours when exposed to natural sunlight. The Colour Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a light source is at rendering colour when compared to a reference light source. The CRI is calculated by comparing the colour rendering of the test source (in this case the lamp) to that of a “perfect” source which in the case of grow lights is the sun. Colour rendering describes how well the light renders colours in objects. Imagine an object that has blue and red, first you illuminate the object with a lamp that has a low CRI and is a cool light source, the red colour will appear dull while the blue will appear rich and vibrant. Now imagine you illuminate the same object with a similar lamp with low CRI but it is a warm light source, the blue in the object will now appear dull while the red will appear rich and vibrant.
  • Wattage (W) – Specifies the rate at which energy is being used to produce light (how much energy in a given amount of time, in units of watts, where 1 watt = 1 joule per second)
  • Efficiency – Indicates how many lumens are produced per watt (lm/W). That is, efficiency is the amount of electricity being consumed to produce light. The higher the efficiency number, the more the savings in electricity!

Most of the parameters described above do tell a lot about a light source, but while you can derive information about how plants will respond to the above measures, it is often not direct, nor simple to do so. As you might imagine, plants don’t particularly care about the light humans perceive, nor how closely light reveals the true colours of an object.

Plants are more interested in the absolute light they can get and use for photosynthesis and other photobiological processes.

What Plants Care About

From the perspective of a growing plant, the characteristics of light (such as intensity and colour temperature) become important only if the radiation they receive is of a type of light that plants can utilize.

Plants rely on harvesting specific wavelengths of light to thrive, which are not targeted by traditional indoor retail lights.

The range of wavelengths plants need for photosynthesis and other growing processes is referred to as photosynthetically active radiation (PAR).

Below is a graph that illustrates different ranges of radiation. Note that plants respond mostly – but not only – to blue and red light at the edges of the visible light spectrum. PAR is a wide range of the spectrum not fully supplied by retail lamps. This is why we should not use technical details of light that pertains to the human eye in order to talk about plant grow lights, and why a different lighting technology altogether is often a better choice for commercial indoor farming.

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Electromagnetic spectrum of light wavelengths from the low level ultraviolet (UV) on into the infrared (IR) wavelengths.

Image Source: inda-gro.com/IG/?q=node/53

Commercial Lights

The wavelengths of light mostly used by plants are at the edges of the visible range. In CEA, commercial lights for vertical farming are built to optimize plant growth, taking into consideration the specific PAR range needed by the crop. As we will see, commercial lights do not rely on light measurements specific to the response of the human eye. Rather, they make use of the latest and deepest knowledge of how plants fundamentally respond to light. Commercial lighting combines factors such as light quality, the intensity and quantity of the light provided and the efficiency of how the light operates – each of which can be tuned for the specific needs of the crop you are trying to grow.

To some extent, it is possible to grow some plants even under household/incandescent light bulbs, but not all light is usable by plants and the type of light that is possible for plants to absorb for photosynthesis is key.

Indoor farming look to provide the best lighting technology available that covers the widest light spectrum that suits the growing needs of the individual plant crop.

You might think that grow lighting is a recent technological branch of the light bulb, but that’s actually not the case. Andrei Famintsyn, a Russian botanist, was the first to use artificial light for plant growth and research in 1868, more than ten years before Edison would patent the light bulb (1879). From the early technological development of incandescent light, there was already a divergence in their application.

Commercial grow lights are applied to many different horticulture forms: from growing exotic flowers, plant propagation, seedling transplanting, food production using indoor hydroponics, aquaponics or aeroponics techniques, insect cultivation and even growing chickens. As we alluded to above, commercial grow lights are designed to provide the proper light spectra for the optimal species growth and development. This article will dive deeper into the factors to consider when selecting a light source for your indoor farm.

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What is Light?

Just as we are dual beings with body and mind, light has a wave-particle dual nature. Light is made up of bundles of energy called photons. Even though photons have no mass (no mass at rest to be precise), they have the characteristics of a particle (such as being able to collide), and they also behave as waves.

The length of the wave oscillation (from one peak to the next) is what we call the wavelength. Wavelength is often written as lambda (λ) and measured in nanometers (nm).

Light is both a wave and a particle. It behaves as an electromagnetic wave in particle quanta (“chunks”) called photons. The wavelength of light is the distance between successive peaks of the electromagnetic wave.

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Image modified from sites.uni.edu/morgans/astro/course/Notes/section1/new4.html

A wide range of wavelengths make up the electromagnetic radiation (EMR). In EMR, the shorter the wavelength, the higher the energy.

Overall, the figure below shows how the EMR waves are categorized in decreasing order of energy as: gamma rays, X-rays, ultraviolet (UV), visible, infrared (IR), radar, and radio waves

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In a strict definition, light is only the part of the electromagnetic radiation spectrum that the human eye can detect (visible light, ~400 nm – 700 nm). However, other portions of the EMR spectrum are also commonly referred to as “different forms of light.” The human eye senses photons in the visible light region, at about 400 nm – 700 nm. A combination of different receptors in our eye, and interpretation by our brain categorizes wavelengths into colours and tones: blue, green, yellow, red, etc. Anything outside the visible region cannot be seen with the naked eye. Note that we refer to approximations (~), with no tight boundaries in the visible light range because people can respond slightly below 400 nm or above 700 nm. We perceive different wavelengths of light as different colours that range from blue, green, yellow, to red. All the different colours of light have different energies, blue being more energetic than red. Plants mainly absorb red and blue light energy for photosynthesis; however, combining red and blue with light of other colours improves plant health and growth.
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Interesting Thoughts on Colour

Ironically, the colours we use to label and identify objects are the colours of light rejected by that object.

For example, if you see a red apple, it is red because the apple absorbs every other colour and scatters or emits only red. Therefore, the apple’s red colour is the wavelength band that it does not absorb.

This aligns with what we know about green light and plants: green light is of limited use to plants compared to blue and red. Since plants absorb small amounts of green, most of the green light is emitted and we perceive the leaves as being green.

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PAR, PPF, PPFD, DLI

The following measures and acronyms were developed in order to better control and quantify light exposure to plants in CEA environments: indoor, vertical and greenhouse farms.

It is important to understand that these acronyms were formulated based on how light is absorbed and used by plants. Aside from the terms mentioned in the retail lamp section above, understanding these terms and using them to evaluate lights are a much better approach when qualifying a light’s suitability for plant growth.

Photosynthetically Active Radiation (PAR)

Photosynthetically Active Radiation, referred to as PAR, is the type of light that plants use for photosynthesis and to drive their development. This is a range within the visible spectrum in the 400 nm – 700 nm.

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There is a popular misconception that plants utilize only the blue and red wavelengths. As seen in the above figure outlining the McCree curve, the type of light that plants use also includes green and yellow radiation.

The most abundant plant pigment involved in photosynthesis, chlorophyll, is most efficient at absorbing blue and red light. Therefore, most of the green light is not absorbed and is reflected by plants, giving leaves their characteristic green-colour. However, plants have other pigments called accessory pigments that include carotenes and xanthophylls. These accessory pigments are able to absorb green light.

Also, plants have physical responses to different types of light.  Photomorphogenesis are structural changes that take place in response to changes in the environment, such as variations in light exposure. Below are some examples of the changes that can be induced by modulating the type of light that plants receive:

  1. 400 nm – 520 nm   Blue Light can inhibit development if not combined with other types of light and can promote leaf thickness. Also chlorophyll absorbs wavelengths in this range.
  2. 500 nm – 600 nm   Green Light penetrates deep and is absorbed more deeply into lower parts of the canopy.
  3. 630 nm – 660 nm   Red Light influences germination, seed formation and plant flowering.
  4. 720 nm – 740 nm   Infrared Light can promote early flowering, also enters more deeply into lower parts of the canopy.

These wavelength ranges only scratch the surface of the myriad of ways scientists have discovered, and are continuing to discover, how plants respond to light.

Should the PAR Spectrum be Revised?

Recent studies suggest that the PAR range should be revised. In spite of the oversimplification that plants require only blue and red light, we know that pants do benefit from green, yellow and other wavelengths outside of what is considered the PAR range.  Even though UV light can cause cell damage to plants by altering their DNA, studies have also shown that UV light can promote plant health by inducing mechanisms of defense.

Likewise, some synergistic effects between wavelengths that were thought to be useless for plants can additionally enhance photosynthesis.

For example, it has been evidenced that long wavelengths (far red light, beyond 700 nm) that interact with short wavelengths (blue light) deep into the canopy can drive photosynthesis.

PPF & PPFD

Photosynthetic Photo Flux (PPF)

With PAR under our belt, let’s say we now can count the number of photons in the PAR range. The number of photosynthetic photons alone, however, does not give us completely meaningful information as there is no specification of how often or how frequently those photons are emitted from a light source.

For example, we can have two lamps that each can output a billion photons. If one of those lamps emits those billion photons in a second, and the other in an hour, we can see they are quite different.

In this case, we say that both lamps give entirely different light fluxes, or numbers of photons per unit time. By considering the time period for photon emission, we create the value known as photosynthetic photon flux (PPF).

Radiant flux is another type of flux that considers the total energy of all photons emitted per unit time . While PPF only considers the number of photons within the PAR range, radiant flux includes absolutely all radiation.

Because blue light has more energy than red light, the same number of blue photons would have more energy than an equivalent number of red photons. Photosynthesis in both cases would be roughly the same (as would the PPF, because the number of photons per second is the same), but the radiant flux would be higher for the blue. Therefore, PPF is a closer direct measure of photosynthesis, and is thus the unit of choice for CEA indoor and vertical farms as well as greenhouse farms. PPF gives an easy and objective comparison of different light sources intended for CEA farming.

However, PPF will not consider the distance and projection of the emitted light striking the crops. Hence, we still don’t know how much light emitted by the light will be received by the plant for photosynthesis.

For example, let’s say we have two lamps that have the same PPF value of 1 billion photons per second. Each lamp’s light is completely absorbed by a plant, but in one case, it’s absorbed by a large plant with giant leaves (for example, monstera deliciosa), while in the other it’s absorbed by a small plant with tiny leaves (for example, a tiny juniper tree). We now see that one lamp would have to have its light more directed than the other, i.e. its light would have to be more concentrated. The concentration of light is referred to as intensity.

From the above example, we can see that photon flux alone is not enough to know if a lamp is suitable – we also need to know how many photons are going to strike our plant, and a specific area of our plant.

To determine the light intensity received by a plant, we need to divide the PPF by the area over which that flux is received. There’s an additional complication that light from a lamp usually spreads the farther it travels, so the measurement of flux will depend on the height of the lamp from the crop.

Photosynthetic Photo Flux Density (PPFD)

To know how much light emitted by a source will be received by the plant for photosynthesis, we calculate the photosynthetic photon flux density (PPFD). PPFD results from dividing PPF by the area it reaches, whose standard units are micromoles per second per square meter (μmol/m2s).

If a lamp produces a high amount of light, it is useless for a plant if those photons never reach the surface of a leaf.

PPFD is the amount of photons that will actually hit the surface in a given time (for the purposes of grow lights, photons within the PAR range of 400 nm – 700 nm). If you have a PAR meter it can capture PPFD measurements.

By measuring PPFD values and comparing to both what is originally emitted at the light source, and what is needed by the plant, a grower can determine the light intensity required for optimal plant growth.

Most interestingly, measuring PPFD values allow growers to closely match a plant’s photosynthetic saturation point, which is where maximum photosynthesis and plant growth are achieved without wasting additional energy.

When plants reach their photosynthetic saturation point, any additional light will be wasted and may even damage the plant.

Again, PPFD measures the intensity of light at a fixed distance from the light source. In CEA, this distance is set as the lamp’s distance from the crop.

For example, if we grab a basic flashlight, we can measure different PPFD values depending on the distance. We will have a large PPFD value when the flashlight is measured close to our sensor (we can use the floor and our eyes as our detector in this case). We will have a low PPFD when our sensor is farther away (i.e. when we point the flashlight far away from the floor). PPFD is strongly correlated to the perceived brightness of a source. Consequently, a light with high PPF that is far away will have the same PPFD as a light with lower PPF that is closer or more directed at the same area.

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With LED lights, we can place grow lights closer to the plant canopy versus other grow light lamp types because LEDs do not generally operate at high temperatures. High temperatures emitted by lamps can damage plants. Placing grow lights closer to plants allows us to use less energy to produce the same PPFD values plants require. If the growth lamps have controllers to adjust the intensity, the height at which the lamp is positioned can be fixed and the PPFD be controlled by dimming or intensifying the light.

DLI (Day Light Integral)

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Once we know PPFD, we can then go further to calculate the intensity of light received by the crops per day. This measurement is known as the daily light integral (DLI). The units are μmol/m2day.

DLI is calculated by multiplying a fixed PPFD value by the number of seconds in a day (i.e. 86,400 seconds), this only applies when PPFD is the same throughout the day.

However, steady PPFD values are rarely the case and usually monitoring systems are required to integrate the total DLI. The integration of PPFD essentially just multiplies each different PPFD by the amount of time that intensity was applied. All the different contributions are then added. Rough calculations can be done manually, but monitoring systems are the most reliable.

Fortunately, a grower can begin measuring DLI for as little as $200”. To measure DLI, PPFD values need to be recorded throughout the day, multiplied by their time duration as described above, and then added to calculate DLI.

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Photobiology: How Commercial Grow Lights Affect Plant Biology

Light is both a source of energy and a source of information for plants.

Light is the source of energy for photosynthesis, the process that gives us the oxygen we breathe. Light is also a source of information that triggers physical changes in plants (photomorphogenesis).

When we want to grow plants inside, though, it is a challenge to provide sufficient PAR light to sustain plant photosynthesis and photomorphogenesis.

Incandescent (and other) indoor light sources provide neither the appropriate light spectrum nor the energy to replace the sunlight that promotes healthy plant growth.

Although household fluorescent lights could support plant growth, they would need to be placed inches away from the foliage and be on for over 16 hours a day. Even then, the plants may not grow well because the spectrum might not have the right wavelength coverage, and the plant may not be receiving the right information from the spectrum.

Commercial indoor grow lights are used to grow plants in enclosed spaces with a spectrum mimicking that of the sun. However, we are not limited to reproducing sunlight. We can actually go a step further and provide a tailored spectrum better suited to the needs of the plant or the type of research being conducted. Plants have different light needs that vary by plant species or their life stage. That is, some plant species may need more light while others do better in the shade, and a seedling requires a different type of light than a plant that is about to bloom.

We can adjust light settings with commercial growth lamps that control the wavelengths (type of light) supplied and the amount that is given to plants.

To better understand why and how plants respond, we have to go into more detail about their biology and metabolic processes.

Photobiology and PAR

Plant metabolism depends on interactions with light. Photosynthesis – the conversion of light into chemical energy – is driven by molecules called pigments that absorb light in the visible range, mostly in the blue and red region.

LED light technology permitted the execution of an experiment where plants were hit with specific wavelengths outside the standard PAR range, something that would be far more difficult with incandescent bulbs. The results suggested that wavelengths higher than the PAR range (above 700 nm) interacting with short PAR wavelengths efficiently triggered photosynthesis. This result is known as the Emerson Effect, where the rate of photosynthesis increases when combining short and long wavelengths.

Indoor grow lamps of good light quality must provide not only radiation in the PAR range, but portions outside the typical range  to reflect our growing understanding of light outside the PAR range.

Furthermore, duration of exposure to light is also crucial and its effects are clear by observing that different plants will preferentially flower during short or long days. An inappropriate or mismatched duration of light exposure can, therefore, cause a plant not to flower. The effect that light duration has on plants is called photoperiodism.

Photoperiodism can influence many physiological processes like seed production, bud dormancy, flowering, flower maintenance, leaf maintenance, plant growth, plant development, crop/fruit yield, and overall quality. For example, ornamental crops grown under optimal light duration have smaller and thicker leaves, shorter internodes, higher root mass, higher branching and flowers.

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7 Types of Commercial Grow Light Sources

We’ve seen some of the specifications and parameters used to characterize grow lights, and there are many different technologies and approaches to try and achieve the optimal conditions for plant growth. As we’ll see below, the type of light source plays a fundamental role in a grow lamp’s achievable specifications.

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Incandescent Grow Lights

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The first kind of light bulb ever invented was an incandescent light bulb. For a long time, they were the lights found in most households. They’re generally sold in your corner grocery or hardware store.

As their name implies, incandescent light sources produce light through incandescence – the emission of light due to heat.

The basic construction of an incandescent bulb consists of placing a filament in a vacuum or inert-gas-filled chamber (the bulb). Incandescence is achieved by passing an electric current through the filament, which will heat up and glow with blackbody radiation. The reason the filament needs to be in a vacuum chamber is to prevent the oxidation of the metal, as well as to prevent overheating. Inert gas, rather than the vacuum, helps slow down the evaporation of the heated filament as well. Incandescent bulbs have been around for over 100 years and Thomas Edison is widely considered to be the inventor.

The reason why incandescent light bulbs became popular is that they do not require any additional equipment beyond a source of electricity. They are also very cheap to manufacture and work well on either alternating current (AC) or direct current (DC).

However, due to the intrinsic physics of blackbody radiation, they are much less efficient than other types of electric lighting for plant growth. A lot of the input energy used to produce light is lost as heat – radiation outside the visible spectrum. The heat production of incandescent bulbs creates a massive issue when considering their use to grow plants; their significant heat production can be harmful to plants.

To avoid damage, therefore, incandescent lights should not be placed closer than 24 inches to a plant. By setting a minimum distance for safe operation, the maximum possible light intensity received by the plant is lowered.

Incandescent light bulbs produce an electromagnetic spectrum that is slightly red-shifted, resulting in plant deprivation of light in the blue spectrum.

Incandescent light bulbs are also relatively short lived, with a lifetime of between 750 hours to 1,000 hours. Although their initial cost will be low, once you take into account how much energy incandescent bulbs consume and how many times you will need to replace them, they may end up being an expensive choice.

If you want to grow healthy plants, incandescent bulbs could be used as a supplemental light source for flowering plants since red light tends to encourage bud and flower growth, but on its own, incandescent light is insufficient for healthy crops in a commercial setting.

Pros and Cons of using Incandescent Lights for Growing Crops in a CEA

Pros Cons
  • Very inexpensive
  • Can be used as supplemental light
  • Do not require special equipment
  • Low efficiency
  • Excess heat production
  • Short life 750-1,000 hours
  • Low light intensity
  • Need to be placed at least 24 inches from plants
  • Red shifted spectrum
  • Halogen Grow Lights

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    Halogen lamps are readily available, inexpensive and easy to find. They are commonly found in most households and are popular for reading or other basic lighting needs.

    They are also known as tungsten halogen, quartz halogen and quartz iodine lamps.

    They are a form of incandescent lamp that is made up of a tungsten filament inside a seal transparent bulb which is filled with a mixture of an inert gas and a small amount of a halogen such as bromine or iodine. The mixture of inert gas and halogen inside the bulb allows the filament to operate at higher temperatures than that of a typical incandescent lamp.

    Because you are able to heat up the filament to a higher temperature you are able to produce light that has higher luminous efficacy and better colour temperature (when compared to incandescent lights). As with standard incandescent bulbs, the high temperature of the bulb can be harmful to plants.

    Another limitation of halogen lamps is that, compared to incandescent bulbs, they produce light that is shifted to the red end of the electromagnetic spectrum, but do not provide as much light from the blue end of the spectrum.

    For this reason halogen lamps are typically used as a supplement to another artificial light or natural light.

    Halogen grow lights have an energy output that is 20% light and 80% heat.

    Because of their extremely high operating temperature (around 2,900 K to 3,200 K) these lights can easily burn a user. This same operating temperature also prevents the bulbs from functioning properly in cold environments.

    They are extremely sensitive to skin oils which can easily cause them to malfunction.

    They last approximately 3,600 hours which is 3 times longer than that of incandescent bulbs but are significantly less efficient than compact fluorescent lamps and LEDs.

    Pros and Cons of using Incandescent Lights for Growing Crops in a CEA

    Pros Cons
  • Higher luminosity than incandescent light
  • Good supplemental light sources
  • Last 3 times longer than incandescent bulbs

  • Low efficiency
  • High bulb temperature
  • Red-shifted light
  • Not appropriate for cold environments
  • Fluorescent Grow Lights

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    Whether tubular or compact, fluorescent lamps produce light by passing energy through a gas in a tube.

    Fluorescent lamps are a low-pressure mercury-vapour gas discharge that apply the physical properties of optical fluorescence to produce visible light. Fluorescence occurs when an orbital electron of a molecule, atom, or nanostructure, relaxes to its ground state by emitting a photon from an excited singlet state. In other words, fluorescence occurs when a substance absorbs energy, goes to an excited state and emits light as it relaxes. The emitted light is what is referred to as fluorescent light.

    In the conventional fluorescent lamp that uses low-pressure mercury-vapour gas discharge, an electric current is used to excite mercury vapour. Mercury vapour fluoresces as it de-excites, and emits UV radiation. On the inside of the fluorescent bulb or tube is a phosphor coating that will absorb the UV radiation (putting the phosphor into an excited state). Finally, the phosphor will de-excite and fluoresce light in the visible range.

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    Image source: researchgate.net/figure/Structure-of-double-capped-linear-fluorescent-lamp-CREE-Inc-2015_fig5_330468620

    Fluorescent lights present an advantage over incandescent bulbs because, despite the two-stage process described above, they are significantly more efficient because they emit primarily in the visible spectrum, rather than having a great deal of excess invisible radiation like the infrared emitted by incandescent bulbs. Fluorescent lights are also available in a range of colours and operate at cooler temperatures.

    Fluorescent lights can be used to produce the light needed by a variety of plants to grow indoors. They come in many shapes and can provide a colour temperature range of 2,700 K to 10,000 K. They typically have a long life span ranging from 12,000 hours to 20,000 hours, with high efficiencies between 75 lm/W to 90 lm/W.

    Despite their many advantages over incandescent bulbs, there are several disadvantages to using fluorescent lights. They are generally not dimmable, because a minimum arc energy is needed to produce the initial mercury discharge, and the discharge is generally controlled by the amount of mercury vapour. Because of the need to have both mercury vapour and phosphor coatings, their fixtures can also be costly. Mercury vapour also implies safety considerations during disposal and possible bulb breakage. Fluorescent lights require a ballast (a device that limits the amount of current in an electric circuit) to start and run the lamp at the correct voltage and current levels (otherwise they flicker, as is often observed).

    Finally, their efficiency declines with frequent on and off cycles, making them not ideal for repeatable plant illumination scheduling.

    Tube-style Fluorescent Lights

    Fluorescent grow lights are usually used for growing vegetables and leafy greens.

    Fluorescent lamps, also known as fluorescent linear tubes, are categorized according to their wattage, shape and diameter. The “T” in T5 indicates the bulb is tubular shaped, while the “5” denotes that it is five eighths of an inch in diameter.

    Standard fluorescent lighting comes in various form factors, including the T5, T8 and T12. The brightest version is the T5 with a yield of ~5,000 lumens and with a power consumption of around 54 watts.

    As mentioned above, a ballast is needed to run these types of lights, in order to start and maintain the lamp at the correct voltage and current.

    Fluorescent lamps have less output power than incandescents and are more appropriate for plants with lower energy needs. There are however, high-output fluorescent lights that produce twice as much light as standard fluorescent lights. A high-output fluorescent fixture has a slim physical profile, making it suitable in vertically restricted areas.

    Pros and Cons of using Tube-style Fluorescent Lights for Growing Crops in a CEA

    Pros Cons
  • Long life (12,000 hours – 20,000 hours)
  • High efficiency ~75 lm/W to 90 lm/W
  • Costly fixtures
  • Flickering issues
  • Require ballast
  • Efficiency decline with frequent on and off
  • Contains mercury
  • Compact Fluorescent Lights

    Compact fluorescent lamps (CFLs) are smaller versions of the original fluorescent lamps described above.

    CFLs specifically designed for growing plants are larger than household CFLs and often have highly reflective aluminum deflectors that direct light onto plants.

    These 110-volt lights (in North America) fit into standard mogul base sockets and do not require ballast. CFLs are available in a range of brightnesses (usually expressed as incandescent-bulb equivalents) such as 125-watt, 250-watt and 300-watt.

    Pros and Cons of using Compact Fluorescent Lights for Growing Crops in a CEA

    Pros Cons
  • Do not require a ballast
  • High efficiency
  • Low initial price compared to tubular fluorescent
  • Low heat output
  • Lower light intensity (Lower growth rates and yield)
  • On and off too frequently can reduce that lifetime substantially
  • Contains mercury
  • High Pressure Sodium (HPS) Grow Lights

    Horticulture Lighting For Commercial Indoor Farming Growers 38

    High-pressure sodium (HPS) lamps are a type of gas discharge lamp that uses sodium in its excited state to produce light. The arc tube is typically made of translucent aluminium oxides which is a type of ceramic. They were first developed in the 1950s for street lighting.

    HPS lights work by having a polycrystalline alumina inside an arc tube that is itself inside a bulb. The arc tube is essentially a pressurized vessel filled with xenon gas and a mixture of sodium and mercury.

    These lamps fall under the category of High-Intensity Discharge (HID) lamps which produce light by sending a series of high voltage electrical pulses between two electrodes at each end of the tube. In order to generate light they need to create a stream of electricity through the xenon gas, which requires a high voltage between 4,000 V and 5,000 V (where V = volts).

    Since regular domestic electrical outlets supply between 110 V and 240 V, a ballast is needed to create the required voltage. The xenon gas, being inert, acts only as a carrier for the electrical flow between the two electrodes. The arc flow produces a lot of heat which serves to excite both the mercury and sodium vapours. Mercury is excited first, and it then fluoresces to produce a blue glow. As the temperature increases, there is enough energy to excite the sodium vapour. Sodium will then fluoresce into an orange glow. The combination of orange and blue light from sodium and mercury, respectively, produces a spectrum with a better white-light colour than would be produced with pure sodium or mercury alone.

    As the arc stream gets more intense, the ballast reduces power to around 250 V. HPS lamps are available in 150 W, 250 W, 400 W, 600 W and 1,000 Watts.

    HPS lighting is very popular in industrial lighting and is also commonly used in grow lighting. They are high-efficiency lamps with a long life rating of 24,000 hours.

    The HPS electromagnetic spectrum is slightly red-shifted, which promotes blooming and fruiting. Because HPS lamps are deficient in blue light, most commercial growers are forced to use both metal halide and HPS lights in order to cover a wider electromagnetic spectrum.

    Most hobbyists use HPS lights as a supplement to natural sunlight to extend the number of daylight hours, or to increase the light intensity during a cloudy day.

    When plants are grown using HPS lights, they tend to elongate due to the lack of blue/ultraviolet light. A disadvantage of HPS is that they have a poor colour rendering index (a quantitative measure of the ability of a light source to reveal the colours of objects in comparison to natural sunlight), which makes it difficult to visually monitor the health of the plant indoors.

    HPS lights also emit a lot of heat which needs to be controlled using air-cooled bulb reflectors or enclosures. Finally, since these lamps contain mercury, when they are broken or disposed of, the mercury poses health and safety concerns for the user.

    Pros and Cons of Using High Pressure Sodium Lights for Growing Crops in a CEA

    Pros Cons
  • High efficiency
  • Long life (~24,000 hours)
  • Useful for blooming
  • Require a ballast
  • Red shifted spectrum
  • Poor CRI
  • Emit a lot of heat
  • Contains mercury
  • Metal Halide Grow Lights

    Horticulture Lighting For Commercial Indoor Farming Growers 39

    Another type of grow light is the ceramic metal halide (CMH) lamp Other names for this light type include light-emitting ceramic (LEC), or ceramic discharge metal halide (MH). However, ceramic metal halide (CMH) is the most common term that we will use.

    To understand the physics of CMH lights, it is easiest to first look at the construction of a traditional metal halide lamp. Like HPS lights, metal halide lamps have an arc tube containing a mixture of gases—in this case, salts and halides in addition to mercury.

    Traditional Metal Halide Lamps

    In traditional metal halide lamps, there are three electrodes in an arc tube. The arc tube is often made of quartz, while the electrodes often contain tungsten. The two main electrodes are very similar to an HPS lamp, with one on each end of the arc tube. The third additional electrode is used to start the lamp, by having an arc discharge between the starting electrode and one of the nearby main operating electrodes. This serves to heat up the bulb contents (which, when cold, have often condensed on the sides). As the bulb heats up, the arc can travel farther and farther until the current reaches the electrode at the other end of the tube. This type of metal halide lamp is called a probe-start type, because of its reliance on this third electrode.

    Horticulture Lighting For Commercial Indoor Farming Growers 40

     Image source: build.ca/part/MP100-U-MED-100W-EDX17-Metal-Halide-Lamp-Clear

    One of the disadvantages of MH lamps is that when you turn them on, tungsten sputters from the electrodes. The sputtered tungsten coats the insides of the arc tube, causing it to darken over time, blocking light and ultimately decreasing lamp performance.

    Pulse-start MH lamps use a high-voltage ignitor with a ballast to turn on the lamp rather than a starting electrode. The pulse-start is preferred over the probe-start type because it provides faster startup, restarts (restrikes) and reduced warm up time. The high-voltage ignitor transfers heat much more quickly and has a longer lamp life, because less tungsten sputtering occurs with such fast heating.

    Metal Halide lamps are very commonly used in the horticulture industry. Because they are blue shifted they are commonly used for the vegetative stage of plant development. They help plants grow stronger roots and healthier leaves.

    Ceramic Metal Halide (CMH) Grow Lights

    Ceramic metal halides are a type of metal halide lamp and like the traditional metal halide lamp, it has an arc tube. Here, however, the arc tube is ceramic rather than the more traditional quartz. The ceramic arc tube is necessary to prevent corrosion by the mixture of salts and halides that are found in the lamp.

    Having a ceramic tube also allows for higher temperatures which in turns allows for a better blend of emitting gases to produce a better spectral match to sunlight. This mixture of salts and halides is what gives this lamp type its more complete spectrum. The spectrum of CMH lamps is much more complete than any sources discussed so far, possessing a CRI of 96 (recall the CRI defined above

    CMH lamps have become popular when compared to HPS lamps because they run at a cooler operating temperature, have improved spectral match and are more efficient. This increased efficiency and lower temperature results in a reduction or even elimination of the need for additional cooling equipment (however, they still run hotter than LEDs).

    CMH lights also have a long lifespan of over 20,000 hours. Additionally, they retain about 80% of their initial light output after 20,000 hours.

    However, CMH lamps are not without their challenges. The CMH light spectrum, while being a good spectral match, also contains UV light of all types. It produces UVA, UVB and UVC bands (but usually a glass filter is used to block the most harmful UVC band).

    Another of the disadvantages of CMH grow lights is their higher initial costs. They cost on average twice as much as comparable HPS or MH systems. However, it is worth noting that a CMH bulb doesn’t use as much power to generate the same amount of light, so over its lifetime, a CMH lamp may have lower operational costs in comparison to HPS and MH lamps.

    However, when compared to LED grow lights, CMH is less efficient and will result in higher cost overtime.

    Finally, one of the biggest disadvantages of CMH lights, is their long warmup time. The various compounds inside the arc tube have a tendency to condense on the insides, requiring substantial time to be reheated into the vapour phase for optimal performance. This prevents rapid turn-on and off of the lights. Intensity adjustments are also difficult, as the tube’s performance is optimized for a specific voltage and current.

    In summary, ceramic metal halide lamps are more efficient and have a better colour spectrum than HPS and MH lamps. They also may have lower lifetime costs despite the initially higher cost of the bulb. They share similar warmup issues with other MH and HPS lamps, as well as the concern over disposal and handling of mercury content.

    Pros and Cons of using Ceramic Metal Halide Lights for Growing Crops in a CEA

    Pros Cons
  • Have a better spectral matchthan HPS
  • Produce less heat than MH or HPS
  • Long lifespan of ~20,000 hours
  • Higher efficiency than HPS and MH
  • Produce more heat than LEDs
  • High cost setup
  • Long warm-up time
  • Hazardous materials for breakage and disposal
  • Require a ballast

  • Induction Grow Lights

    Horticulture Lighting For Commercial Indoor Farming Growers 41

    Induction grow lights are unique because they use electromagnetic fields Instead of filaments to transfer power to the light’s emitting material. Because filaments wear out, induction light bulbs last much longer than filament-based light sources.

    There are two types of induction lighting; plasma grow lights and magnetic induction grow lights.

    Plasma Induction Grow Lights

    Plasma grow lights use microwave radiation to excite sulfur and create a plasma, a cloud of ionized gas. The emission of the hot plasma de-exciting provides the spectrum for these grow lights.

    However one of the issues with sulfur plasma emission is that it is missing important parts of the electromagnetic spectrum (peaks around 500 nm) that plants need to be healthy.

    Another issue that you may encounter with plasma grow lights is that the band of electromagnetic radiation used by plasma grow lights is similar to that used for Wi-Fi, so the lights may interfere with Wi-Fi functionality and othe RF interference.

    Magnetic Induction Grow Lights

    Magnetic induction grow lights produce a more complete light spectrum. They are very similar to fluorescent lights with the difference that they do not have a filament. Instead, the filament is replaced by magnetic induction to ignite the phosphorus.

    Horticulture Lighting For Commercial Indoor Farming Growers 42

     Image source: tzlight.com/technology

    Because they do not have a filament and the filament is usually the first thing to break in fluorescent bulbs, magnetic induction lights therefore have a longer life.

    Magnetic induction lights can run for up to 100,000 hours. They do not lose light intensity nearly as fast as MH or HPS grow lights, and they do not require long warm-up times.

    However, there are several disadvantages to magnetic induction lights.

    They have poor light penetration, therefore they can never replace an MH/HPS setup. They are relatively expensive when compared to other grow lights. They do not have built-in cooling options – which forces the need to install a separate cooling system.

    They are less efficient than HPS systems which results in less light for the same amount of electricity which in turn means higher cost of operation. They are typically used as supplemental grow lights or as replacements for fluorescent light systems.

    Induction grow lights have remained pretty much unchanged since they were first demonstrated in the 1800s.

    In summary, other than their unique way of producing light by using electromagnetic fields, when compared to LED or MH/HPS systems, induction grow lights significantly underperform.

    Pros and Cons of using Induction Lights for Growing Crops in a CEA

    Pros Cons
  • Long life, up to 100,000 hours
  • Do not lose light intensity as fast as HPS or MH
  • Do not require warm up time
  • May interfere with WiFi
  • Poor light penetration
  • Low efficiency
  • High cost
  • LED Grow Lights

    Types-of-Grow-Light-Sources-led

    Light emitting diodes (LEDs) were first used in a single source grow light more than 20 years ago. Lettuce was grown under red LED light combined with blue light provided by fluorescent lamps.

    LEDs are solid-state light emitting diodes, and as such, are more robust and longer lived than traditional light sources that are made of fragile filaments, electrodes, or gas filled pressurized lamp enclosures.

    Light-emitting diodes are made from a very thin layer of doped semiconductor material and depending on the semiconductor material used and the amount of doping, an LED will emit a coloured light at a particular spectral wavelength.

    LEDs work by having electrons from the semiconductors conduction band recombine with holes from the valence band releasing sufficient energy to produce photons which emit monochromatic light. Because of this thin layer a significant number of photons leave the junction producing a colored light output. Light Emitting Diodes are semiconductor devices that convert electrical energy into light energy.

    The composition of the LED semiconductor material will determine the overall wavelength of the photon light emissions and therefore the resulting color of the light emitted. Today, the entire visible spectrum can be covered by light‐emitting semiconductors:

    Horticulture Lighting For Commercial Indoor Farming Growers 43

    Image source: tofasterinfo.wordpress.com/%E5%8D%9A%E5%AE%A2/chapter-1-led-basics/led-basic-structure-light-emitting-principle/

    Additionally, LEDs can be designed to emit broad or narrow-band light tailored for a desired plant response. Tuning an LED to the absorption peak of a specific plant pigment allows generation of a specific plant response without any waste energy producing unused broadband spectra.

    One of the most important features of LEDs is the fact that they are on a solid chip and can therefore use a heat sink to manage waste heat. This is in contrast to other lights such as incandescent or halogen where the high temperature is an intrinsic, inseparable part of the light source. The ability for LEDs to separate waste heat from the source of illumination becomes especially important for high intensity LEDs. This decoupling allows LEDs to be placed close to plant canopies without the risk of overheating and stressing plants.

    When compared to high intensity discharge lamps that emit significant amounts of heat and require considerable separation from plants in order to avoid heat stress, LEDs present a significant advantage.

    The waste heat from LEDs can be transferred and distributed for use in greenhouse heating which offsets the cost of fuel during cold weather, or allows venting during warm weather.

    Pros and Cons of using LED Lights for Growing Crops in a CEA

    Pros Cons
  • Produce almost no heat
  • Full light spectrum
  • Customizable light spectrum
  • Long life over 50,000 hours
  • Do not require a ballast
  • Narrow band emission (for specific pigments)
  • Can be used continuously
  • Very high efficiency
  • Environmentally-friendly
  • Produce directional light (cover less area)
  • High initial cost
  • Cheaper LED lights can change colour as they age
  • Light Source Summary

    Most types of grow light sources produce heat, not just light, which needs to be taken into account when growing plants. If plants are placed too close to your grow lights they can suffer from heat stress and localized low humidity.

    LED lights produce far less heat, and the heat they do produce can be decoupled through heat sinks and redistributed elsewhere. Therefore, LED lights can be placed closer to plant canopies than high intensity discharge (HID) lights. LED grow light technology could be the best candidate for achieving the correct intensity and spectrum of light without heat stressing your plants.

    The most commonly used lights for professional plant growth are HID and fluorescent light bulbs, but LEDs are becoming more and more popular due to their efficiency and economy.

    Additionally, LEDs are environmentally friendly, can be used to create custom spectrums, can be easily turned on and off, produce very small amounts of heat, do not require a ballast to operate, have long lamp lifetimes and modern LEDs are now available in the full visible spectrum. For these reasons LEDs are quickly replacing the use of fluorescent and HID grow lights in grow operations.

    Horticulture Lighting For Commercial Indoor Farming Growers 44

    Grow Lights for Vertical Farming

    The modern concept of vertical farming was initially proposed by Professor Dickson Despommier at Columbia University in 1999. Despommier and his students came up with a design for a farm to be built in a skyscraper that could feed 50,000 people.

    This design popularized the idea of vertical farming.

    Horticulture Lighting For Commercial Indoor Farming Growers 45

    The main advantage that vertical farming provides is the ability to increase crop yield while requiring a smaller area of land.

    The Association for Vertical Farming, highlights that vertical farms use 98 percent less water and 70 percent less fertilizer on average than outdoor farms. Additionally, since crops are intended to be indoors in vertical farming, they are not subjected to weather disruptions or unexpected weather occurrences. As an added bonus, vertical farming’s minimum land usage is far less disruptive to native plants and fauna.

    In theory, vertical farming is an agricultural technique involving large-scale food production in indoor structures that enable more efficient plant production by controlling environmental conditions and nutrient solutions to crops based on hydroponics.

    According to Wikipedia, there are three main types of vertical farming:

    One of the challenges often highlighted in vertical farming is the amount of energy required to grow plants inside a building since vertical farms within buildings have less access to natural light. There is therefore a need for energy-efficient artificial lighting with a broad electromagnetic spectrum.

    This challenge has been recently overcome by the advances in LED lighting.

    Horticulture Lighting For Commercial Indoor Farming Growers 46

    How to Compare Light Sources for Commercial Indoor Growing

    Comparing indoor growing lights can be a burden, but it doesn’t have to be if you know what features you need to compare.

    Knowing what is important to the plant simplifies the process of comparison between lamps. That will help dissect manufacturer information and choose the pertinent data for comparison purposes.

    Take, for example, the colour rendering index (CRI) that measures the ability of a light to reveal a colour. While such a metric may be important to attract our attention towards a bright colourful red apple, it is not important when choosing a lamp for plant growth. The CRI might still be helpful to consider if a grower needs to assess plants by their leaves’ colours to monitor , for example, lack of nutrients or over fertilization. This information is helpful for the grower, but not necessarily for the plant’s development.

    The table below provides a broad overview to compare different types of light sources.

     LifespanCRIEfficiency Lumen/WattCold Weather Use RecommendedHeat Emission
    Fluorescent grow lights20,000 Hours80-9070-105

    No

    (Slow Output)

    ~30%
    Incandescent grow lights1,000 Hours100Less than 20

    No

    (Extremely inefficient)

    ~90%
    HPS Grow lights24,000 Hours20-3060-140Yes~50%
    Ceramic metal halide grow lights20,000 Hours90-9665-115Yes~15%
    Induction grow lights100,000 Hours ~80Up to 100YesProduce small amounts of heat
    Halogen grow lights1,200 Hours10015-20No~80-90%
    LED grow lights60,000 HoursUp to 99Up to 300YesAlmost no heat
    Horticulture Lighting For Commercial Indoor Farming Growers 47

    Full Spectrum LED Grow Lights

    Lamps that emit in the 400 nm – 700 nm PAR range are called “full spectrum”. Full spectrum lamps emit light in all colours, covering the whole range (with no significant gaps in that range) from ultraviolet to infrared. Some lights only supply a combination of blue and red, and lamps that fail to provide radiation of all colours are not considered to be full spectrum lamps.

    Dual red and blue LED grow lights have become popular as they cover the range where plants absorb light most effectively. However, plants also utilize regions of green and yellow and grow light manufacturers are broadening the radiation that lamps provide. Most LEDs now include “white” and this can be observed as lamps are shifting away from the pink that resulted from the blue/red light composition. Also, we know that wavelengths outside the 400 nm – 700 nm region can also contribute to positive effects in plant growth and some lamps can also supply radiation that includes regions below 400 nm or above 700 nm.

    We now know that green and yellow light as well as wavelengths outside the 400 nm - 700 nm region also contribute to the photosynthesis and photomorphogenesis process in interesting and complex ways.

    Thus, full spectrum lighting is ideal for CEA farming.

    Horticulture Lighting For Commercial Indoor Farming Growers 48

    Dynamic full light spectrum allows you to tune the amount of energy across the visible spectrum of colors so that it can better fit your needs.

    Hence dynamic full light spectrum lights are proving advantageous over limited fixed spectrum lights, allowing for quick changes in lighting conditions to adapt to multiple plant stages and differing needs during a plant’s life cycle. 

    Horticulture Lighting For Commercial Indoor Farming Growers 49

    Growth characteristics that can be affected using full spectrum lighting are listed below:

    • Fruiting
    • Flowering yield
    • Rate of growth
    • Fresh weight
    • Compactness
    • Root development
    • Colour
    • Flavour
    • Germination
    • Nutrition
    • Plant health

    Other interesting application of dynamic full spectrum lights include the ability to manipulate the concentration of terpene in cannabis plants. By eliminating red light during the last 3 days of growth, phytochromes (a class of photoreceptor in plants) are inhibited, resulting in terpene (fragrant oils that give cannabis its aromatic diversities) accumulation in the maturing trichomes (which are fine outgrowths or appendages on plants).

    Recent developments on LEDs have enabled them to emit light that ranges from ultraviolet to infrared light by using different semiconductor materials. This renders LEDs with the advantage over other light sources of providing a full spectrum.

    Horticulture Lighting For Commercial Indoor Farming Growers 50

    How to Compare LED Grow Lights

    As more LED grow light models and styles develop, the more difficult it is to make a fair comparison. This section’s purpose is to provide the criteria to properly compare these LED lamps and make informed decisions.

    There are many physical characteristics that will suit different horticulture setups. For example, if the lamp is thick, round, squared, or how much it weighs. Even though these parameters are worth considering they should not be the primary drivers when choosing a grow lamp..

    But when it comes to light, a fair comparison is to evaluate the light quality, the amount of light it emits, how much of it will actually get to the crops and how much energy is needed for the lamp to produce this radiation .

    The overall suitability of a LED grow light can be evaluated by the following light characteristics and by asking the right questions based on plant science.

    Light Quality: Spectrum Range

    Horticulture Lighting For Commercial Indoor Farming Growers 51

    You need to know that the lamp is providing the spectrum of light that plants need. That is, make sure the lamp emits photosynthetically active radiation (PAR, at least 400 nm – 700 nm) in the region of the light spectrum most utilized by plants you are looking to grow.

    Ask: What is the grow light spectrum range? Does the lamp emit at least in the 400 nm - 700 nm (PAR) range?

    Light Intensity: Required Power per Area

    Another parameter you need to consider when investigating grow lights is the watts per square meter (W/m2) required for your specific growing needs. For example, tomatoes require between ~320 – 540 watts per square meter to produce healthy high quality crops. You can calculate how many watts per square meters you will have by dividing the number of watts supplied by the light source by  your growing area (more information link)

    Light Quantity: How many Photons reach the Plants

    The fact that a lamp emits light in the PAR region, does not necessarily mean it will be available for the plant. Therefore, it is important to know the amount of PAR light that will reach the plant. The amount (or intensity) of light hitting the plant will vary according to the plant’s distance from the lamp.

    Horticulture Lighting For Commercial Indoor Farming Growers 52
    Sample list of PPFD required at stages of plant growth
    Light quantity can be evaluated by measuring the number of photons in the PAR region that hit an area at a fixed distance (photosynthetic photon flux density, PPFD). It is typically measured in micromoles per second per square meter  (µmol/m2/s). Where μmol is a unit of counting based on Avogradro’s number (6.02 x 10^23 photons = 1 mol, 6.02 x 10^17 photons = 1 umol),

    Ask: What is the grow light’s PPFD at your target distance? (remember that intensity varies with height, so compare and rate different lights under the same conditions)

    Light Efficiency & Efficacy

    A key parameter for growers to determine operating costs is to know how much energy is required to generate light (in the PAR range) that is usable to plants. The efficiency of regular/retail lamps is assessed in lumens per watts (lm/W). In commercial growth lights, the efficiency is measured by photosynthetic flux density per watt (PPF/W) and it is known as photosynthetic photon efficacy, PPE. PPE indicates the power that is required to produce PAR light in units of µmol/J.

    Photosynthetic Photon Efficacy (µmol/J) refers to how efficiently a lamp can convert electricity into radiation that can be used by plants. That is, how much power is required to generate that flux of photons:

    Horticulture Lighting For Commercial Indoor Farming Growers 53

    The electric power required to run a grow light is measured in watts (W), where 1 joule = 1 watt per second. The higher the wattage (power), the more electrical energy is consumed. Power multiplied by time gives the total energy used, which is why the units of the above equation become µmol/J.

    A deeper explanation can be found here.

     

    A good comparison between LED grow lights should consider the light quality, light amount, and efficiency. Below is a table that  you can use to capture manufacturer specs and help in the comparison process:

    Ask: What is the PPE? Hint: the higher the number, the higher the efficiency!

    Manufacturer

    Light Quality (Wavelength Range)

    Spectrum range (min should be PAR) (nm range)

    Light Quantity (PPFD)

    PPFD (at fixed  height) (µmol/m2/s)

    Efficacy (PPE)

    PPE (µmol/J)

    A)   
    B)   
    C)   

    TODO Is it possible to add a chart here too to compare these 3 critically important factors to use when finding the right commercial light? LED Light? 

    Horticulture Lighting For Commercial Indoor Farming Growers 54

    Dynamic (or programmable or tunable) full light spectrum lights are proving advantageous over limited fixed spectrum lights, allowing for quick changes in lighting conditions to adapt to multiple plant stages and differing needs during a plant’s life cycle. 

    Horticulture Lighting For Commercial Indoor Farming Growers 55

    Choosing a Specific Grow Light Spectrum for Plant Growth Stage

    In order for plants to grow using indoor lighting, it is important to control the spectrum under which they are illuminated.

    There are violet LED lights currently on the market. These only offer blue and red light, and ignore the rest of the PAR spectrum. Therefore, they do not efficiently stimulate plants.

    Although plants absorb red and blue light strongly, it does not mean they do not use or need the rest of the PAR spectrum. In fact, the use of green light in horticulture is increasing. The benefits of a full spectrum light varies from better visual inspection in white light, increased plant growth, increased biomass, and more.

    Outside of photosynthesis, the reason plants react to different colour spectrums is due to changes in sunlight depending on the time of day and the season of the year. Plants have evolved to use the spectrum to get information about what’s happening in the world around them.

    If we consider seasons, for example, more blue light reaches the plants during spring and summer because the sun hits the earth directly. As fall approaches, the sun hits the earth at a greater angle and more blue light is lost. The higher amount of red light reaching the earth is a signal to the plants that fall is starting, and the plant should therefore begin preparations for winter.

    If we consider the time of day, plants track far red to red light ratios to determine the start and end of day. At sunset, far red light continues striking the plant for a longer time than red light, effectively increasing the far red/red ratio until night begins. At dawn, far red/red ratios decrease as the sun is about to rise. Once the sun has risen, blue light reaches the plants and the day has begun. Plants can use this information to know when they can expect to receive light for photosynthesis, or not.

    With dynamic full spectrum lighting, you can completely control colour spectrum ratios and purposely influence a plant’s cycles and behaviour. You cannot do this with fixed narrow band LED lights or other types of lamps.

    A significant advantage of full spectrum tunable LED lights, is their dynamic control of almost any operating parameter.

    Flexibility is an important characteristic for any grow lighting system as no plant has the same colour spectra for growth, flowering, maturation, and more.

    While plants can and do survive off a single spectrum of illuminated light, their life cycle and growth are far from optimized under such circumstances. Plant growth and development can be optimized by varying spectra depending on the type of the crop and the current stage of the plant. Still, the best light conditions vary both by the plant and also the grower’s needs and more can be found in this scientific paper.

    With flexible lighting solutions, a farmer can now adjust colour spectra and light intensity dynamicallythus maximizing crop yields, quality, and flavour.

    Horticulture Lighting For Commercial Indoor Farming Growers 56

    There is No Universal Plant Light/Colour Spectrum

    Plants have different light requirements at different stages of their development, and because plant species all have slight variations in their developmental processes, different light/colour recipes are constantly being developed and updated to maximize different stages of growth in a plant species.

    Grow Light Recipes

    Farmers have historically tuned parameters within their control, and usually that didn’t involve control over sunlight. They therefore relied strongly on the control of other ingredients such as element ratios in nutrient solutions, temperature and humidity.

    However, plant development is highly influenced by more than these ingredients, and especially by the light it receives. Light has an effect over different plant characteristics which can be modulated by tuning a plant’s illuminated radiation.

    As scientific research and plant growth technology progress, we can have more precise control over the desired features in a plant crop.

    Horticulture Lighting For Commercial Indoor Farming Growers 57

    Some plant characteristics and processes that can be influenced are the production of phytoceuticals (medicinal molecules such as cannabinoids, terpenes and flavonoids), plant stages such as flowering, plant development like branching and elongation, and plant productivity (in terms of biomass and yield).

    Throughout a plant’s life cycle, light has a different effect depending on the plant’s stage of growth stage. For example, on germination, plant height/elongation, budding, etc. As technology advances, we can provide specific light spectra as ingredients or instructions to direct plant growth.

    What Specifically is Being Tuned in CEA Grow Light and Environment?

    The ratios of blue, red, greens, along with temperature, humidity and PPFD. This varies by plant species and by a grower’s desired results. Some light recipes can be found here TODO hyperlinkhttps://scynceled.com/spectrum-tuning/recipes/

    Below, we present a quick review of colour spectrum recipes for cannabis, lettuce, and strawberry.

    Cannabis General Light Recipe Theory

    Since cannabis is one of the most profitable crops to grow, there are multiple sources where one can learn about cannabis growth with full spectrum LED lights. If you are just starting to understand and account for the full effects of the colour spectrum, cannabis has well understood cycles and is a great crop to investigate first.

    Cannabis reacts to different colour spectrums in order to germinate, grow and make buds. As a cannabis plant gets exposed to a higher amount of red light, it reacts by growing longer stems with more space between the leaves, getting as tall as possible for the best position to start making buds and pollinate. Additionally, plants may switch to the flowering stage faster under red light than blue.

    If we look at blue light, grow lights with a higher amount of blue light are often used in the vegetative stage as they tend to make cannabis plants grow short and squat, with big healthy leaves. Blue light also has an effect on when germinated seeds switch from root growth to seedling, opening leaves.

    Finally, UV lights may increase THC levels or other potency aspects of cannabis buds, since we know that UV-B light does change how plants grow. However, we don’t know exactly how yet, and there is still much to learn for this crop and many others. This unknown scientific territory allows growers the potential to create their own colour spectrum recipes as trade secrets to give them competitive advantages.

    Tree Transplanting General Light Recipe Theory

    TODO

    Insect Growth General Light Recipe Theory

    TODO

    Lettuce General Light Recipe Theory

    TODO

    Strawberry General Light Recipe Theory

    TODO

    Horticulture Lighting For Commercial Indoor Farming Growers 58

    LED Lighting Trial/Test

    If you’re a master grower, changing the technology and tools used in your facilities can be a daunting task. Making the switch from HID or other traditional lamps to LED lights can seem overwhelming at first, but we’re here to help you see that the process is not only worthwhile, but easier than you might expect.

    Now that you know what LED lights can do for you, we can talk about some practical ways you can get the most out of your grow lights. A small experiment will yield a lot of information to inform and optimize your grow light setup. You will be empowered to make changes for your specific target outcomes.

    Before setting up a trial, ask yourself the following questions:

    1. What plant process(es) are you interested in optimizing?

    2. It is very important to know what you want to achieve with your grow lights. Remember that the visible light spectrum contains red, orange, yellow, green, blue, indigo and violet. Usually colours on either end of the spectrum play the biggest role in plant development. Blue light is often used during a plant’s growth stages such as when seeding (and when flowering is not desired). Red light, on the other hand, promotes flowering. Furthermore, not all plants need the same light intensity or irradiation time. So once you know what plant process(es) you want to optimize, you can move on to determining the best ways to measure those processes.

    3. How do I gather data on the processes I’m interested in?

    4. Next, you need to decide on the measurements needed to best answer your questions. For example, if you’re trying to maximize leaf size, you will want to regularly measure leaf area. Or if you’re trying to maximize the number of buds, you will want to regularly count the number of buds. If possible, try to figure out a way to get the plant measurements you need in the shortest period of time using sensors and automation.

      Once you know the measurements that will indicate whether your light is improving or diminishing your target plant processes, set a consistent interval time for taking the measurements. Do not forget to take into account the plant’s growth cycle when planning both the measurements and the intervals.

    5. What are the most likely spectra changes to optimize my target process(es)?

    6. If you’ve read this entire article, you’ve sampled some of the different ways plants respond to light of different spectra. You’ve gotten an introduction to some of the guiding principles of photobiology.

      You are now equipped to make some educated predictions about what light spectra your plant of interest might prefer. Write down your prediction and make sure your grow lights will allow you to test your prediction by turning on or off the spectral regions of interest.

      LED lights allow you to test a variety of light recipes to best isolate the optimal conditions for your target processes. They also allow you to be really specific in testing and comparing geographic conditions. For example, if you are trying to study the effects of increased UV light irradiation on strawberry flowering in Canada, you can set up your desired intensity to vary only in the UV, and otherwise match the irradiation time to match the day length in Canada throughout the year.

    7. Do you need a control area?

    8. Yes. In order to measure the effect of your light changes, you are going to need a control area where the light spectra changes is not applied. You need to set up an area that will remain unchanged throughout the duration of your experiment, with all the same conditions as your initial experiment setup..

    9. How should I set up a trial area?

    10. Once you have designated a control area, you need to designate a separate area for your trial. This area should have identical conditions to the control area and should allow you to change your setup without affecting the control area.

    11. OK, what now?

    12. Gather measurements for both the trial and the control area, and compare! You have the data to assess whether your educated hypothesis on how to improve the plant’s biological processes were correct or not, and are in a position to refine for further tests.

    Horticulture Lighting For Commercial Indoor Farming Growers 59

    Calculator ROI for Your Grow Light Investment

    Allocating funds for an LED commercial grow lighting solution can be a difficult decision for a business, where the return on investment (ROI) might not be as clear as you’d like it to be. We’ve developed a set of criteria to help you determine the value to expect out of an LED grow light.

    1. Step One: Determine the PPFD required for your plant(s)

    2. If you have existing lights, you can measure what they currently provide your plants in terms of PPFD. If you don’t have existing lights, you can do a bit of research to determine the optimal PPFD for your intended growth plant(s). (If you don’t know what PPFD is, check here)

    3. Step Two: Determine the total area coverage you need

    4. You need to know the target area of all of your plant growth, in order to determine how many lights you need.

    5. Step Three: Determine number of lights needed

    6. Grow lights will specify either PPF or PPFD at a specific distance, so once you know the total area you need covered, you can calculate the number of lights needed to achieve the required PPFD coverage.

    7. Step Four: Determine the total electrical power required to run the lights

    8. The grow light’s efficacy will tell you how much power is needed to achieve the desired PPF. If you have an existing grow light operation, you probably already know what you annual power consumption is for running the lights, and will be able to compare.

    9. Step Five: Convert power to electricity cost

    10. Once you know the total power required, you can calculate the annual cost by multiplying the estimated number of operating hours per year, and the average cost of electricity per kilowatt-hour (kWh). The savings will be the difference between the two annual operating power numbers:

      Annual Savings = # of lights X Hours used per year X kWh Rate X ( (Existing lighting system wattage — New lighting System Wattage) / 1000 )

    11. Step Six: Calculate ROI

    12. Then you can calculate the ROI which is typically displayed as a percentage. You can think of this as the percentage of the investment that the new lights will return in profit in a year.

      ROI (%) = ( Annual Savings) / ( # of lights X cost of lights ) * 100

    13. Step Seven: Calculate Payback Period

    14. To calculate the payback period (number of years it would take for the new lighting to make up for the investment) you can:

      Payback Period (Years) = ( # of lights X Cost per light ) / Annual Savings

    Other factors to consider In addition to calculating simply calculating the ROI for the saving in electrical cost, you also need to take into account the following factors:
    • HVAC cost
    • Typically about 30% of the energy used for indoor growing goes to HVAC
    • How often you have to replace the bulb
    • HPS bulbs have to be replaced about once a year whereas LED lights will last up to 10 years or more
    • Different lighting systems for different plant stages may provide crop yields beyond the financial considerations calculated above
    • LED lights can provide a full spectrum unlike other lighting systems, which will give you the tunability and flexibility to grow your plants in a more ideal manner than you have before

    Depending on other factors you may want to consider, there are alternative methods to calculate ROI. Hopefully the process above can serve as a starting point from which to roughly estimate how good or bad the lighting investment may be.

    In our examples, we tried to use data representative of reality and real customer installations. As you can see from the numbers we used, the ROI shows that the lower operational cost over X years justifies the initial investment into LED fixtures.

    Horticulture Lighting For Commercial Indoor Farming Growers 60

    Horticulture Lighting Conclusion

    Controlled Environment Agriculture (CEA)

    Vertical farming is one of today’s growing trends. With the technological advances for Controlled Environment Agriculture (CEA), such as the development of full spectral coverage with LED lights, it is possible to bring sunlight indoors and completely control the development of your plants.

    Indoor Farming Grow Lights

    Indoor farm grow lights should be optimized for plant growth. Plants rely on harvesting specific wavelengths of light to thrive and most lights found at retail stores lack the spectrum plants need to survive and thrive.

    Photobiology

    Grow lights have different effects on plant growth development. By modifying the spectral range, light intensity and quantity and duration, growers can modify different plant attributes such as:

    • Time of flowering
    • Branching
    • Growth (root/shoot elongation)
    • Increase yield (biomass and produce)
    • Boost plant defense systems
    • Amount of phytoceuticals

    To learn more about photobiology click here.

    Light Sources: Types of Commercial Grow Light Sources

    There are many types of commercial growth lights for horticulture, and they can either supplement another source of light (for example, supplementing sunlight inside a greenhouse), or completely replace sunlight (for plants growing in enclosed spaces like vertical farms):

    • Fluorescent grow lights
    • Incandescent grow lights
    • HPS grow lights
    • Ceramic metal halide grow lights
    • Induction grow lights
    • Halogen grow lights
    • LED grow lights
    LED lamps comparison

    Main parameters to consider when comparing LED lamps:

    • Light quality – Spectral range – look for full spectrum light (broad radiation, PAR range)
    • Light quantity – How much light actually gets to the plant (PPFD)
    • Lamp efficiency – The power required to emit the quality of light (PPE)
    Horticulture Lighting For Commercial Indoor Farming Growers 61

    Resources

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    Horticulture Lighting For Commercial Indoor Farming Growers 16

    Frequently Asked Questions

    Question?

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