[] s_{er}(\lambda)
The standardized relative spectral effectiveness in producing erythema (evaluated 24 hours post-exposure) on sensitive human skin of type 1 (always burn, never tan) and type 2 (usually burn, sometimes tan).*

s_{er}(\lambda ) = 1.0    for    250 \leq \lambda \leq 298 nm

s_{er}(\lambda ) = 10^{0.094(298-\lambda )}    for    298 \lt \lambda \leq 328 nm

s_{er}(\lambda ) = 10^{0.015(140-\lambda )}   for   328 \lt \lambda \leq 400 nm

Note: The absolute dose required to produce a given degree of erythema varies enormously in the range 250 nm to 298 nm, especially below 280 nm. Consequently, for the sake of simplicity and as a ‘reference’ to compare erythemal efficacy of different UV sources, a uniform spectral sensitivity was adopted for wavelengths below 298 nm.**


* A Reference Action Spectrum for Ultraviolet Induced Erythema in Human Skin, CIE Publication 106; 106/4. Vienna, Austria: International Commission on Illumination; 1993.

** IESNA Photobiology Committee. Recommended Practice for Photobiological Safety for Lamps and Lamp Systems – General Requirements, ANSI/IESNA RP-27.1-15. New York: Illuminating Engineering Society of North America; 2015.

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