Safety glasses with impermeable lenses prevent dirt. Factory workers need thick glasses and a sturdy frame with sidebars. The welder must wear special protective eyewear that protects him from sparks and lightning strikes on the torch.
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Sports glasses are lightweight and flexible. They can bend without breaking under pressure and then return to the correct shape. Sunglasses can have a prescription or over-the-counter lenses.
Lenses are colored to reduce discomfort and damage caused by bright light and ultraviolet (UV) light. Tinted lenses in sunglasses increase the contrast between color and depth of perception.
There are several types of special glasses. One such type is 3D glasses which mislead the viewer into seeing three dimensions on a flat surface. This is done by providing different information for each eye.
Glasses usually have a red lens on one side and a green lens on the other. Popular 3D glasses for watching horror movies or sports adventures. Another special type is glasses with two or three focal points on the same lens. These glasses add to the inconvenience of having different glasses for different activities.
Often the lenses do not show a gradual change in focus. Other people cannot get used to graduated glasses, so they need different glasses for each job or hobby.