Note 1 to entry: For in-vitro testing, the erythemal irradiance measured by a detector with the fabric sample under test in place is compared to the erythemal irradiance measured with no fabric present, where the source is typically a solar simulator. This is expressed as the quotient of the erythemal irradiance without fabric to the erythemal irradiance through fabric:

${\displaystyle F_{\text{UVP}}=\frac{{\displaystyle \underset{\text{290 nm}}{\overset{\text{400 nm}}{\int }}{E}_{\lambda }{s}_{\text{er}}(\lambda )\text{d}\lambda }}{{\displaystyle \underset{\text{290 nm}}{\overset{\text{400 nm}}{\int }}{E}_{\lambda }{s}_{\text{er}}(\lambda )\tau (\lambda )\text{d}\lambda }}}$

where s_er(λ) is the erythema spectral weighting function, E_λ is the spectral irradiance, τ(λ) is the measured spectral transmittance of the item, and λ is the wavelength.

Note 2 to entry: The ultraviolet hazard spectral weighting function, S_UV(λ), has been substituted for s_er(λ) in special instances. If so used, the ultraviolet protection factor, F_UVP, has to be noted as F_UVP [S(λ)-weighted].

Note 3 to entry: The ultraviolet protection factor has unit one.