Significance: There is substantial scientific uncertainty about the necessary levels of protection in sunglasses to avoid delayed health effects from solar ultraviolet radiation in the ultraviolet A (UV-A) band. The longer-wavelength limit for UV-A and the inclusion of the spectral effectiveness function in the calculation of solar UV-A transmittance are questionable.
Purpose: There has been a wide range of informed opinion with regard to the level-or even need for-near-ultraviolet filtration (by absorption or reflection) in sunglasses. Many current sunglass filter lenses transmit very little near-ultraviolet radiant energy, whereas others transmit a significant fraction. There also are opposing commercial interests that argue either for strong filtration or for minimal protection. We review the evidence for potential risks and the challenge for the designer of any sunglass lens. It is shown that current standards are not at all cautious in their requirements for near-ultraviolet protection and do not meet a philosophical approach of minimizing needless exposure to optical energy that does not benefit vision.
Methods: The arguments for and against various factors in eye protection from ultraviolet radiation are discussed. The solar UV-A transmittance of some sunglass and clear spectacle lens materials has been calculated using the formulae and methods used in the International Standards Organization sunglass standard. The Annex gives results of the calculations both with and without the S(λ) erythemal weighting function and up to 380 or 400 nm.
Results: The solar UV-A transmittance calculated with the S(λ) function and only up to 380 nm gives numerical results that are lower than taking either the upper limit for UV-A as 400 nm or without the S(λ) function.
Conclusions: Most sunglass lenses will still pass the requirements with the more stringent requirements, but some spectacle lens materials will need extra treatment.