In 1978 the Subcommittee on Photovoltaic Electric Power Systems of ASTM Committee E-44 (TODO this one? https://www.astm.org/COMMITTEE/E44.htm ) started developing standard methods for measuring the electrical performance of photovoltaic devices. In 1985 a series of revised ASTM standards were finally available.
Solar simulators are fundamental for photovoltaic measurements being done in both research and industry, and since the illuminated current vs. voltage (I-V) is sensitive to the spectrum, intensity and temperature, looking for new light sources and developing higher accuracy optical systems based on the leading standards became a priority.
Additionally, standard PV solar simulators had issues with lowering the average power and temperature fluctuations (caused by prolonged exposure to the light). As solar cell manufacturers started to ramp up manufacturing, large area simulators that were capable of testing modules were developed. To minimize power use and excessive heat generation, the illumination times were reduced, decreasing the measurement time. As a result of trying to solve this issue, the pulsed solar simulators were designed and developed. In parallel, additional solar simulator development continued, including development of multisource simulators for improved accuracy, high intensity simulators for multijunction and concentrator systems, and LED systems. With the development of high power LED technology in the 1990s, solar simulators were developed to use this new light source, which offered advantages such as tunable spectra, high accuracy, long operating life, and output control of the light source with a 30- 50 nm resolution. LEDs consume less energy, pack much smaller than conventional lamp based housing and LEDs can be controlled within microseconds or operated stably at one light output intensity continuously for a long time. (TODO ref https://www.diva-portal.org/smash/get/diva2:756274/FULLTEXT01.pdf)