Sunglasses are used by people, mainly due to protect eyes from sunlight, ultraviolet rays, and visible light, which have high energy. Sometimes Shade sunglasses are used for the visual purpose, which has polarized, colored, and darkened lenses, which also known as spectacles. These Shade sunglasses are also called sun cheaters because it protects against sunlight.
Shade sunglasses provide a unique function, which is that it provides prevention from excessive light exposure in terms of both visible and visible components of sunlight. Exposure with ultra-violet rays has very dangerous effects on the human body like pterygium, snow blindness, photokeratitis, cataracts, and many other types of eye cancer.
Medical experts have given public awareness on the Shade sunglasses' importance that it should wear during sunlight. Medical experts also provide awareness to people that Shade sunglasses filtered out or provide prevention about 99 percent or more of UVB and UVA light, which have wavelength about 400nm, so that is why these sunglasses also known as "UV400".
These eye glasses are not providing sufficient or permanent protection against sun light. There are special eyeglasses that are used during a solar eclipse and used for viewing the sun directly, and these sunglasses are known as solar viewers.
If someone wants to evaluate sunglasses protection so he/she must measure lenses that are used in sunglasses. These lenses are measured by either an optician who is properly equipped or by a manufacturer. Medical experts can identify whether sunglasses meet the protective requirements against sunlight or not.
In the early 12th century, sunglasses were used by Chinese people, and these sunglasses are made to by flat panes with smoky quartz, which prevent eyes by glare while these sunglasses do not have corrective powers.