May I compliment Zeiss on improving the UV protection of their lenses
May I compliment Zeiss on improving the UV protection of their spectacle lenses to absorb up to 400nm (Optician, January 11).
There is a slight misconception in the article, in that BS EN ISO 8980-3 governing spectacle lens transmittance, does not require absorption up to 380nm, only that averaged values of UV-A transmittance for solar radiation are calculated up to 380nm.
On this basis, clear standard CR39 absorbs 93% of UV. Changing to 400nm, it absorbs 85%, while additionally removing the spectral weighting factor that ICNIRP states should not be used, it still absorbs 55%.
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