Blog – Why is Class AAA Important?

Why is Class AAA

Whether using an artificial illumination source for photovoltaic characterization, photochemistry experiments, or environmental testing, the quality of your light will have a major impact on the quality of your data. When searching for a solar simulator you will continuously come across the term “Class AAA” rating – but what does it mean? If you’re not quite sure what that is, and how it applies to your research, we have the answer.

The standards are set by governing bodies such as ASTM, IEC, and JIS and are used to determine the quality and accuracy of a solar simulator’s illumination. Some classes you may see range from Class C to Class AAA, depending on the solar simulator – which may lead one to think that a Class AAA simulator is better than a Class A simulator. In fact, “Class AAA” is a shorthand for three different parameters of the standard, meaning Class A Spectral Match, Class A Spatial Uniformity, and Class A Temporal Stability.

While the ASTM, IEC, and JIS standards vary slightly, the overlapping minimum requirements for each Class are tabulated below.




What is Spectral Match?

A measure of the amount of light produced within specific wavelength bands compared to the standard spectra and reported as “spectral mismatch”.

Spectral Mismatch To All Intervals

0.75 – 1.25

0.6 – 1.4

0.4 – 2.0

What is Spatial Uniformity?

The distribution and consistency of irradiance over an area.

Spatial Non-Uniformity (%)




What is Temporal Instability?

The temporal stability of a solar simulator is the consistency of light output over a period of time. Thus this instability is the level of unstable light output. 

Temporal Instability
Short Term (%)




Temporal Instability
Long Term (%)




Class A Spectral Match

The spectral match is a measure of the amount of light produced within specific wavelength bands compared to the standard spectra and reported as “spectral mismatch”. Most research uses the AM1.5G spectra which defines six regions between 400 – 1,100 nm – however, research in different environments (like in space – AM0, on the surface of Mars, or sub-surface) each have different spectral profiles. *some simulators like G2V pico Variable have tuneable spectra which can be software controlled to replicate all of these conditions and more.

The Class A spectral match requires a factor of 0.7 – 1.25 between the artificial light source and the standard spectra in each wavelength region. If your research focuses on improving the efficiency of solar cells for energy production, you can improve the link between your results and real-world application by utilizing the precise spectral match provided by a Class AAA solar simulator.

Class A Spatial Uniformity

Spatial uniformity describes the distribution and consistency of irradiance over an area. The parameter is reported as “spatial non-uniformity” and is calculated from the difference of the maximum and minimum irradiance values in an area.

Non-Uniformity (%) = (Maximum irradiance – minmum irradiance) / (maximum irradiance + minimum irradiance) x 100

Non-Uniformity (%) =

Spatial uniformity is crucial to ensuring an even distribution of light across an entire experimental area. Solar simulators may have a total illumination area that is much larger than the Class A uniformity area, so it’s important that the high-uniformity area can cover your samples. 

Class A Temporal Stability

Temporal Stability is the consistency of light output over a period of time. Traditional solar simulators (e.g., Xenon, metal halide, or tungsten bulb-based lamps) are notorious for changing spectra and drifting intensity over time, whereas more advanced LED technology has substantially better stability and longer lifetime. Whether performing experiments that require several months of continuous light or when testing multiple devices consecutively, you would require the lowest temporal instability in order to gather accurate data on the performance of your devices.

When it comes to choosing the right solar simulator for your research, the Class AAA rating is necessary, but not sufficient! It’s important to consider how the limitations in the classifications may impact your results, especially if your research is sensitive to changes in time or responds to different spectral ranges. Get in touch with our expert team at G2V Optics to learn more about how our Class AAA Solar Simulator, the pico can benefit you and advance your research.