As defined in ISO 9050 or EN 410, the UV transmittance of glass is calculated with the equation below:
In the equation above:
- τUV: UV transmittance
- λ: wavelength
- τλ: spectral transmittance
- SλΔλ: normalized relative spectral distribution of the UV radiation (part of the standard global solar radiation)
The wavelength range of interest is 300 nm – 380 nm. The term SλΔλ is the weights used in the weighted average of the spectral transmittance. The standard values of SλΔλ are plotted in the figure below.
The peak of the UV radiation distribution is at 375 nm. Glasses with high spectral transmittance near 375 nm are with high UV transmittance.
There are some small differences between the ISO 9050 and EN 410 UV distributions. The UV transmittances calculated according to the two standards could be slightly different.