Sunglasses may be made with either prescription or non-prescription lenses that are darkened to provide protection against bright visible light and, possibly, ultraviolet (UV) light.
Figure 67: Sunglasses Figure 68: Sunglasses.
Photochromic lenses, which are photosensitive, darken when struck by UV light.
Figure 69: Photochromic lenses. Figure 70: Photochromic lenses.
Figure 71: Photochromic lenses.
Figure 72: Light polarization glasses.
ight polarization is an added feature that can be applied to sunglass lenses. Polarization filters remove horizontally polarized rays of light, which eliminates glare from horizontal surfaces (allowing wearers to see into water when reflected light would otherwise overwhelm the scene). 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.
Yellow lenses increase color contrast and improve depth perception. They are worn by people driving at dusk, but are detrimental to vision at night. Any tint further reduces incoming light to the retina, and yellow tints also reduce glare-recovery times for night drivers. Brown lenses are 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 lens with UV protection for times where sun protection is needed.
Sunglasses are often worn just for aesthetic purposes, or simply to hide the eyes. Examples of sunglasses that were popular for these reasons include teashades and mirrorshades. Many blind people wear opaque glasses to hide their eyes for aesthetic reasons.