The sun transmits visible blue and visible violet rays, as well as UV rays which are undetected by the naked eye. The UV rays pose the most potential for damage. An important consideration when purchasing sunglasses is the light transmission factor. It is recommended that lenses should not transmit more than 30 percent of visible light. In areas where light is intense, as little as 10 to 15 percent transmission is preferred.
Manufacturers frequently attach a tag to sunglasses stating the transmission factor.
Other good choices are brown or green tints. Poorly made glasses will not damage the structure of your eyes, but flaws and distortion may cause your eyes to work harder.