A variety of sunglasses exist for different purposes. Generally, sunglasses are used to protect the eye from ultraviolet rays (UV) and other types of harmful natural radiation. Sunglasses should be worn daily, even in cloudy weather. Severe problems like cataracts, cancer, and eye growths can be caused by UV radiation.
Sunglasses come with various lens prescriptions to fit different vision needs. For instance, protective bifocals can be worn at the beach while one is reading. The right sunglasses should offer 100% UV protection. Sunglass lenses are made from various types of plastic and glass material. The bigger the glasses, the better because they offer a comprehensive coverage of the eyes.
Types of Sunglasses
Anti-ultraviolet ray sunglasses
Some sunglasses can block at least 99% of ultraviolet rays, although some do block it 100% (sometimes written as 400nm). Serious ailments such as cancer and cataracts can result from exposure to ultraviolet rays. There are two types of radiation, UVB and UVA. The most dangerous radiation is UVB. A special lens coating is applied to the lens material (either plastic or glass) during the manufacturing process, which can absorb the harmful UV light.
Ground & polished sunglasses
Some sunglasses are nonprescription. They are ground and polished for lens quality purposes. Nonprescription sunglasses that are not ground and polished are useful as well and will not cause any harm. However, the wearer must be sure of the glasses' quality, which is easy to check. S/he can view a rectangle-shaped object, say a tile on the floor, with the sunglasses. The wearer covers one eye from a comfortable distance and moves the sunglasses slowly from one side to the other and up and down. Straight lines indicate the sunglasses are of good quality, while wiggly lines, particularly in the middle of the lens, show the lens are of poor quality.
Impact-resistant sunglasses are designed to withstand the impact that can shatter them. The Food and Drug Administration (FDA) recommends that all sunglasses must be made of a material that is impact-resistant. All lenses are breakable, but plastic material tends to resist breakage more than glass when hit by objects such as stones or balls. Although some sunglasses may not break, they can be affected by scratching. Plastic is used to make non-prescription sunglasses. Most sunglasses for sports activities are made from polycarbonate plastic material but can scratch easily. Some sunglasses made with polycarbonate plastic are scratch-resistant due to the coating used.
Polarized lenses in sunglasses
Sunglasses made with polarized lenses help with driving or fishing. These lenses prevent glare from reaching the eye. They are combined with a substance that blocks UV light. Labels on the sunglasses will show whether they offer maximum protection against UV light.
Lens darkness sunglasses
Sunglasses ideal for very bright conditions are fitted with a darker lens.
Photochromic lenses are suitable absorbents of UV light. These lenses automatically become dark in bright light and lighten in low or dim light. Photochromic lenses take time to adjust to different light situations. For instance, it will take approximately five minutes for the lenses to lighten and 30 seconds to darken.
Wraparound sunglasses help to keep UV light from entering the eyes. A wraparound pair of large-framed sunglasses can protect the eyes from all angles.
Sunglasses made from these types of lenses help protect against glare. They are shaded from top and bottom toward the middle. They come in two types. Single-gradient lenses enable clearer vision, especially when driving, as they do not dim the dashboard's view. However, they may not reduce glare at the beach or in snowy conditions. Double-coated lenses are lighter in the center and dark both on top and bottom. They are suitable for sports because light reflects up off the snow or water. However, they are not ideal for driving since the dashboard appears dim.
Mirror coated sunglasses
Mirror-coated sunglasses have ordinary lenses that have thin layers of metallic coatings. These may not fully protect against UV radiation.
Anti-infrared rays sunglasses
These sunglasses help to block out infrared wavelengths and can come with or without prescription sunglasses.
These sunglasses are said to block blue light and are especially popular with hunters, pilots, boaters, and skiers. They are said to cause objects in the distance to appear more distinct, especially in haze or snow. These lenses cause the environment to appear orange or yellow since they amber and block all blue light.