Skin sensitivity was discovered by Diffey and later adopted by the World Health Organization.
The low-cost UV sensors that have been available for the past 60 years were designed to monitor UV curing of adhesives. To be used by consumers for sun exposure monitoring, UV sensors need to have the same spectral sensitivity to UV as human skin. In 1987, McKinlay and Diffey quantified skin sensitivity across the UV spectrum, from 280 nm to 400 nm. The result is the “erythema spectrum” (EAS), shown above. In summary the EAS says that UVB (280 - 310 nm wavelengths) are exponentially more harmful than UVA (310 - 400 nm wavelengths).
When UV radiation is measured through the erythema spectrum, its outcome is “erythemally-weighted” UV. UV risk is communicated in units of the UV Index or UVI. An irradiance of 25 mW/m2 of erythemally-weighted UV has been defined to be 1 UV index, by the World Health Organization.
The spectral sensitivity of UV photodetectors is due to the combination the photodetector and the filter on top of it. UV photodetectors are usually made of silicon carbide, gallium nitride, or aluminum gallium nitride. We have designed our proprietary photodetector with a polytype 6H silicon carbide which offers very high resistance to degradation generated by both high and long-term UV exposure. Our custom filter was designed to correct the default sensitivity of the detector to closely match the erythema spectrum.