The special Tinted Lenses
Tinted lenses have been bathed in tint colours and can assume just about any colour shade or colour density. The tinted lens actually absorbs the tint colour into the lens material. Tint density is defined as a percentage, where 0% is completely clear, and 100% permits no light to pass through (solid). A 10% to 20% tint is used for a “fashion” tint, and a 50% to 80% tint is used for outdoor protection from the sun.
UV protection filters out the sun’s ultraviolet rays that are very damaging to the eyes. An extra coating is required for hard resin lenses. However, all polycarbonate, high index, and sun-sensitive lenses already include UV protection due to the characteristics of the lens
Unfortunately, many sunglasses sold by street vendors to not comply with UK Law. Using a tinted lens without UV protection can be extremely dangerous. Lens tint has the effect of increasing the wearer’s pupil size and admitting more ultraviolet light to the intraocular lens, which can cause premature cataracts and/or permanent damage to your eyes.
The colour of the tint determines the parts of the light spectrum that are absorbed by the lenses. Manufacturers use different colours to produce specific results.
Gray tints are great all-purpose tints that reduce the overall amount of brightness with the least amount of colour distortion. Gray lenses offer good protection against glare, making them a good choice for driving and general use.
Yellow or gold tints reduce the amount of blue light while allowing a larger percentage of other frequencies through. Since blue light tends to bounce and scatter off a lot of things, it can create a kind of glare known as blue haze. The yellow tint virtually eliminates the blue part of the spectrum and has the effect of making everything bright and sharp. That’s why snow glasses are usually yellow. This tint really distorts colour perception, which makes it inappropriate for any activity that relies on accurate colour.
Amber and brownish tints are also good general purpose tints. They have the added benefit of reducing glare and have molecules that absorb higher frequency colours, such as blue, in addition to UV rays.. These sunglasses also distort colours similar to yellow lenses, but increase contrast and clarity.
Green tints on lenses filter some blue light and reduce glare. Because green tints offer the highest contrast and greatest visual acuity of any tint, they are very popular.
Purple and rose tints offer the best contrast of objects against a green or blue background. They make a good choice for hunting, target sports and water skiing.
Many manufacturers employ a process called constant density to tint the lenses. It is the oldest method of creating sunglasses and involves a glass or polycarbonate mixture with a uniform colour throughout the material. The tint is built right into the lenses when they are created.
Tinting can also be accomplished by applying a coat of light-absorbing molecules to the surface of clear polycarbonate. The most common method for tinting polycarbonate lenses is to immerse the lenses in a special liquid containing the tinting material. The tint is slowly absorbed into the plastic. To make a darker tint, the lenses are simply left in the liquid longer
