information about Sunglasses
may be made with either prescription or non-prescription lenses that
are darkened to provide protection against bright visible
light. Good sunglasses should also protect against ultraviolet
light. Because of changes in the atmosphere, ultraviolet levels are
much higher than in the past and ultraviolet protection for eyes and
skin is even more important. It is possible to have lenses that look
very dark and yet offer little ultraviolet protection. Sunglasses
vary greatly and many offer more style than protection.
lenses, called photochromic
lenses, become darker in the presence of UV light.
Unfortunately, many car windshields protect the passengers from UV
light while not shielding from bright visible light, making
photochromic lenses ineffective where they are most needed. Still,
they offer the convenience of not having to carry both clear glasses
and sunglasses to those who frequently go indoors and outdoors
during the course of a day.
is an added feature that can be applied to sunglass lenses.
Polarization filters remove horizontal rays of light, which can
cause glare. Popular among fishermen and hunters, polarized
sunglasses allow wearers to see into water when normally glare or
reflected light would be seen. Polarized sunglasses may present some
difficulties for pilots since reflections from water and other
structures often used to gauge altitude may be removed, or
instrument readings on liquid crystal displays may be blocked.
lenses are commonly used by golfers and shooters for their contrast
enhancement and depth perception properties. Brown lenses are also
common among golfers, but cause color distortion. Blue, purple, and
green lenses offer no real benefits to vision enhancement and are
mainly cosmetic. Some sunglasses with interchangeable lenses have
optional clear lenses to protect the eyes during low light or night
time activities and a colored lenses with UV protection for times
where sun protection is needed. Debate exists as to whether
"blue blocking" or amber tinted lenses have a protective
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