ULTRAVIOLET RADIATION
There has been a lot written lately on the potential harmful effects of ultraviolet radiation, especially with the "depletion of the ozone layer". Although our predicted demise may be premature, there are a few things we can and should do to protect ourselves from excessive exposure. We all know the result of laying on the beach for hours during midday, and many of us know the result of snow-skiing without the proper eye protection. The sunburn comes as a result of over-exposure to UV-B radiation. This is the shorter wavelength, higher energy, and more dangerous portion of the ultraviolet band. UV-A, or the longer, lower energy band, is responsible for tanning and the photosensitivity reactions. UV-C radiation is rarely encountered on earth except for artificial sources such as an arc welder.
A closely fitted pair of plastic spectacle lenses actually absorbs up to 93% of UV radiation. A similarly fitted pair of glass lenses only absorbs about 55% of UV. If your glasses slip down your nose a mere 6mm, your plastic lenses will now keep just 65% of the UV from entering the eyes. The obvious lesson here, if you are UV conscious, is to wear PLASTIC and have them FIT WELL and close to your eyes. With the addition of a UV coating on your glasses, you may eliminate 99% of all UV radiation. The darkness of your sunglasses has NO effect on the amount of UV radiation that reaches the eye. There have been several studies that actually showed that a clear pair of plastic glasses offered MORE protection from UV than a dark pair of sunglasses of the same plastic! This may have been due to the slightly larger pupil behind the dark lens. The lesson here is to be sure that ANY sunglass has the extra UV coating applied.
The color of your sunglasses is a matter of personal preference. The popular "Blu-blockers" have had significant "infomercial" time, but their claim of "blocking out harmful blue light" may be a bit exaggerated. They certainly do block out the blue light, but the jury is still out on its possible harmful effects. If you don't mind losing your perception to blue, it can be a rather comfortable sunglass. A gray colored sunglass does not alter your perception of color but in a very dark shade it may reduce contrast. Green will definitely change your color perception and may even make traffic signals difficult to recognize. Yellow shades have been popular with hunters and trap shooters for their potential increase in contrast and acuity. Remember that all these colors have little effect on the amount of UV radiation being absorbed by the eye. The fit, size, and UV absorptive qualities of your sunglasses are most important.