PHOTOCHROMATIC LENS?
These lenses are transition or light adaptive and change colour in response to UV light levels.
POLARIZED LENS?
These lenses are designed to reduce glare.
VISIBLE LIGHT TRANSMISSION (VLT)
Categories 0 to 4 in percentage of visible light transmission
Category 0 = 80 to 100%VLT - generally safety glasses that are clear or with a very light tint.
Category 1 = 49 to 79%VLT - casual use cosmetic and fashion eyewear
Category 2 = 18 to 45%VLT - general level of sunglass lens with good UV & visible light protection
Category 3 = 8 to 17%VLT - high UV & visible light protection but may not be suitable for riding on dull days.
Category 4 = 3 to 8%VLT - special purpose sunglasses for extreme glare situations eg snow or water