The S.P.F. number dates from 1978, when the Food and Drug Administration proposed that manufacturers label sun-care products with codes from 2 to 15, based on how long they would multiply time in the sun before burning. Until 1986, the highest S.P.F. available was 20. New technology has made the top number of 1978 virtually the bottom number for cautious outdoors people of 1996, though higher and higher S.P.F.'s provide smaller and smaller increases in protection. And, . . . UV, or ultraviolet, radiation in sunlight is linked to eye disease.
Price has no bearing on UV light protection.
UV light protection comes from a chemical coating applied to the lens, not from the color or darkness of the lens. Polarized lenses cut reflected glare and are useful for driving and fishing. Polarization has nothing to do with UV light protection, although many are now combined with a UV-light blocking substance. Large-framed wraparound sunglasses can protect your eyes from all angles, as opposed to ordinary eyeglass frames that may allow light to enter. And . . . . . .