More than 60 research institutions and companies have proposed standardized testing procedures for indoor solar cells, reporting their framework in Nature Energy.
Indoor photovoltaic devices operate under low irradiance levels ranging from 15 to 330 microwatts per square centimetre. While theoretical power conversion efficiency limits exceed 50 percent under artificial light, inconsistent testing setups have produced performance discrepancies reaching 60 percent in relative terms.
The consortium recommends adopting the CIE LED B-3 spectrum, corresponding to 4,000 Kelvin neutral white light, as the future primary reference standard. Current technical specifications under IEC TS 62607-7-2:2023 use LED B-4 at 5,000 Kelvin. Commercial installations heavily favor 4,000 Kelvin lighting, representing 80 percent of products from supplier Signify and 83.3 percent of European commercial installations. In the United States, commercial lighting consumed 168 terawatt-hours in 2024 compared to 76 terawatt-hours in residential buildings.
Standardized light levels
The framework establishes 200 lux as the mandatory baseline illuminance level for performance reporting, designated as BPIM-B3-200lx. All 15 surveyed commercial indoor photovoltaic manufacturers report device performance at 200 lux. The researchers recommend secondary measurements at 1,000 lux for bright commercial settings and 50 lux for dim environments.
Measurement systems
The guidance outlines specific hardware requirements for light-tight enclosures, recommending pseudo-collimated light sources and interior coatings with less than 3 to 5 percent reflectance. For adjusting light intensity, direct electrical power control yields efficiency measurement ambiguities of approximately 2 percent, compared to 6 to 15 percent for optical attenuation filters. When modulating intensity by distance, the setup requires a minimum separation of 30 centimetres between the light source and the device under test unless optics are used.
