Outdoor light can be 25 times brighter than indoors. Look for lenses that block both Ultra Violet A and UVB
Sunglasses should transmit only 15 to 35% of the available light. Test them in the store by trying them on and looking for your eyes in a mirror. If you can see your eyes the lenses are probably too light
Lens color choices depend on what environment you will be wearing them.
Gray prevents distortion so that colors remain true.
Green allows high levels of green-yellow light waves, the ones to which the eye is most responsive.
Brown and brown-amber absorb blue light waves, which is refracted on hazy days to improve contract and reduce glare.
Cool Blue and Warm Yellow are mostly for fun although some yellow tints enhance contrast.