In the market filled with diverse products, it is nearly impossible to find a pair of sunglasses with clear lenses. Almost all sunglasses come with tinted lenses in different ways. That is for sure that UV protection is the key function provided by sunglasses. And in fact the degree of UV protection is determined by the lens material used and some additional lens treatments. Various tints only determine the darkness of the lenses. But this factor does not determine directly the capability of UV protection the lenses have. With this explanation, some people may wonder that why these lens tints are so popularly used, like a rose, a yellow tint, green tints and gradient tint sunglasses. Remember that different tints have specific degrees of darkness, which determine the amount of sunlight that is allowed to pass the lenses.
There are generally two ways to tint sunglass lenses. Some manufacturers add a substance such as metal oxide to the lens material during lens production. The other way is more popular that surface application allows a wide variety of tints and creates different darkness across the lenses. Most sunglass lenses are tinted in the second way, including gradient tint sunglasses. The intensity or darkness of a tint is expressed as a percentage of the light that is allowed to reach the eyes. It is well-known that sunglasses are used for different purposes, ranging from pure fashion enjoyment to outdoor sports. A fashion tint usually blocks 10-20% of sunlight. Outdoor activities and daytime driving require related lens tints to have an intensity ranging from 70-80%. 90% tints are suitable for sports like climbing and snow skiing.
Among all types of tinted sunglasses, gradient tint sunglasses are quite special that they have different degrees of darkness from the top to the bottom. Rose tint sunglasses, gray tint sunglasses and some others all use tinted lenses that have a uniform darkness across the entire lens. Dissimilarly, a gradient tinted lens has a dark tint at the top, and fades gradually to little or no tint at the bottom. This design allows the lens to block more sunlight coming from above, without blocking too much light from straight ahead or below. A variation of this design is double gradient tint lens, which has a darker tint at the top and bottom, and a medium tint in the center part.