What are the lens categories about?
The sunlens categories are to help consumers understand how much light is transmitted through the lens and how much UV protection is likely to be provided. It shows that very high transmission rates are really only for “cosmetic” purposes and offer little protection. As the light transmission reduces, the sunlenses become more useful for brighter conditions, through Cat 2 and 3.
Cat 4 is at the extreme end and these lenses would be used in environments where there might be unrelenting snow glare, for example. Cat 4 lenses have a very low light transmission rate and are not suitable for driving.
These categories don’t take the lens material into consideration. (The NXT®/Trivex® material, used for Bigatmo lenses, inherently blocks all wavelengths up to 395 Nm, which includes UV A,B and C, and that is before considering the effect of the “tint”.)
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