Sunglasses are a type of tinted lens, but all are not equal.
Spending a great deal of money on designer sunglasses does not ensure that they have good UV or IR filtering, nor does a particular color choice of lens ensure proper protection. They may be cosmetically appealing, but decidedly harmful to the eyes.
To begin looking for the proper type, recall basic physics.
Radiation extends from the minuscule gamma rays, beyond x-rays, ultraviolet, visible light, infrared, all the way up to the very long radio waves. It is no coincidence that the visible light to which our eyes are sensitive is precisely the same radiation which is reflected from such solid objects as trees, rocks, and people. Some of the radiation from the sun, or artificial sources, is harmful to our biological design.
There are two kinds of radiation to which we are normally exposed and which may cause eye problems: ultraviolet (UV) light and infrared (IR).
Both are invisible as far as the eye is concerned, but infrared can be sensed as heat by the skin. The human body has no sense organ that can detect UV, but its absorption on the skin leads to tanning or burns. There is another distinction between the two: UV effects are cumulative over time, but IR is not. Therefore, the ageing and cancer risk on the skin from UVs is related to repeated exposure.
UV rays are almost totally absorbed by the cornea, with some reaching the retina. Macular degeneration is thought to result from UV absorbed by the retina, which causes the surface layer of the cornea to blister and become excruciatingly painful. This happens when people read at the beach or under a sunlamp. They forget that the UV is reflected off the paper and onto the eyes.
Chronic exposure to UV and perhaps IR, has been implicated with the development of cataracts in the lens of the eye. in addition, there is a host of commonly prescribed drugs which can make the eyes more photosensitive and susceptible to injury. All of this makes one realize the importance of eye protection, especially in the use of sunglasses.
Non-prescription sunglasses, the ones bought at a supermarket or drugstore off the “rack,” can sometimes cause more harm. If you are not informed, there is no way for you to know that protective glasses need certain coloring and coatings in order to be effective. The color of the lens is not what counts; rather it is the chemical ingredient added to the lens to produce the color.
For example, a dark green glass properly made will absorb virtually all the harmful rays while another green lens without the proper ingredients, will not. Worse yet, because the imitation lenses reduce the visible glare (nature’s “red flag”), it actually may be more harmful than not wearing colored lenses.
This is like an eclipse situation. The glare is blocked, but not the infrared that passes on through into the eyes. Some of the worst sunglasses are made for children. At the very least, ultraviolet protection should be listed on the glasses. However, that does not address the problem of infrared or cheap and vision-distorting lenses.
The best all-round sunglasses contain properly made dark grey or dark green glass lenses. The smokey-grey tint allows colors to be seen almost normally, but the green filters out a bit more UV and IR.
Blue and yellow, regardless of how dark, are not good choices for sunglasses. However, yellow lenses may be used to increase visibility on a cloudy or hazy day. They enhance contrast by filtering out the somewhat scattered, out-of-focus blue light from the scene. Hunters, pilots, and tennis players find them helpful for this purpose.
Polarizing sunglasses will significantly reduce glare coming off such flat surfaces as water. They are popular with fishermen. Their UV shielding is adequate, but the IR protection is poor.
Blue Blockers is a category of sunglasses that filter out UV as well as the blue end of the spectrum which is alongside the UV. These sunglasses remove blue light, causing colors to appear false and may be annoying to some. They are inappropriate for those who need good color discrimination or for those who have a color deficiency. Along with the apparent clarity they might bring to some, there may be errors made in distance judgment as objects will appear closer, plus there is no IR protection.
The following is a guide for specific uses and the lens color that provides the best protection for that activity.
- Baseball, Football, Soccer, and other outdoor action sports (medium green, grey, or brown)
- Beach Vacation (dark green or grey, with UV and IR filter)
- Boating/Sailing (dark green grey, or brown, with added mirror coating)
- Computer Screen (light tint, with anti-reflective coating)
- Fishing in bright sun (dark green, grey, or brown, with polarizing filter)
- Golf (green or grey on sunny days and amber or gold/yellow on cloudy days)
- Hunting (gold/yellow, with anti-reflective coating on cloudy days; and green or grey in sunlight)
- Night Driving (anti-reflective coating)
- Offices with bright overhead lighting (light to medium gradient tint in rose, brown, or pecan)
- Piloting (dark green or grey gradient with UV filter)
- Racquetball (amber or gold/yellow, with anti-reflective coating)
- Sewing/Needlecraft (light rose, brown, or pecan, with anti-reflective coating)
- Skiing/Snowmobiling (dark green, grey, or brown, with added mirror coating and/or UV coating)
- Tennis (amber or gold/yellow indoors or cloudy days; green or grey on sunny days)