What is the relationship between lens tint vs UV blocking in aviator sunglasses?
We often get questions about the relationship between lens tint and the amount of ultraviolet light (UV) that the lenses block or absorb. Most think that the darker the lens tint the more the UV rays are blocked and the better the protection for your eyes.
I’m sorry to be the bearer of bad news but it simply is not true! The amount of UV radiation protection sunglasses provide is not related to the color and darkness of the lenses.
The amount of uv radiation that a pair of lenses block or absorb is determined by the lens material and any films applied to the lenses rather than the lens tint. In fact it might surprise you to learn that a pair of clear glass lenses can block a fair amount of uv radiation without any tinting at all!
Let’s Talk About Lens Tints
Lens tint is the color that a pair of aviator sunglass lenses have. For example lens tints can be of any color imaginable and can be lighter or darker colored (less or more density).
A lot of times buyers think that when they look at the lenses in a pair of sunglasses that the darker the tint the more protection for their eyes from harmful uv radiation.
Actually, lens tint has more to do with visible light transmission and little or no relationship to uv protection.
Darker lenses will widen the pupils in your eyes need to open in order to see through the lens. Without good uv blocking your eyes can be at risk for serious injury from uv radiation. When your pupils are wide open more unblocked uv radiation will enter your eyes causing damage. Over time this situation can lead to very serious eye damage!
So when you consider a new pair of aviator sunglasses don’t just consider how dark the lenses look, but rather examine the sunglasses to make sure that they will block uv radiation.
Let’s Talk About Lens Materials
Aviator sunglasses – in fact any glasses or sunglasses – all have lenses in them. When thinking about uv blocking the real question is what material are the lenses made of?
There are 7 common lens materials used in all glasses and sunglasses:
- CR-39 Plastic;
- Crown Glass;
- High-Index Plastic;
CR-39 lenses are composed of allyl dilycol carbonate, a polymer invented in 1942. Plastic CR-39 lenses were the 39th formulation produced by PPG Industries which patented the material in 1945. CR-39 plastic readily absorbs tints but scratches quite easily. This is why the lenses are normally coated with an anti-scratch film. The optics are excellent but plastic lenses will absorb only about 88% of harmful uv radiation and therefore need to have a UV coating applied to the lens.
Crown glass lenses provide the best optics of any material and absorb 20% of UVA and 79% of UVB radiation. This means that roughly 20% of uv radiation will pass through the lens and reach your eyes. In order to improve uv blocking a film is added to glass lenses in order to achieve 98-100% uv blocking. On the downside glass can shatter quite easily so today the lenses are chemically treated or heat tempered for strength.
High-Index plastic is similar to CR-39 but can be formed thinner and lighter to accommodate prescriptions that require more correction in order to achieve 20/20 vision. Again, plastic lenses will require a UV film to provide adequate uv protection.
Polycarbonate is a relatively soft thermoplastic material which means it absorbs impact rather than shattering like glass will. Polycarbonate lenses scratch easily and should be purchased with a scratch-resistant coating. At the same time polycarbonate lenses offer 100% protection .
Trivex is a urethane based material which shares many of the same properties as polycarbonate and will absorb 100%of UV radiation. Trivex lenses are one of the best choices for eyeglasses, sunglasses and sports eyewear and aviator sunglasses, as well as the best choice for children and adults where eye safety is a concern.
Tribrid lenses are a newer version of Trivex and the 3rd lightest lenses after Trivex and polycarbonate. Just like polycarbonate and Trivex Tribrid lenses absorb 100% of UV radiation.
Lens tint is important for many reasons but need not be considered when thinking about uv radiation protection.
Don’t let darker lenses fool you into thinking they offer more protection from UV rays, either. The darkness of the lens does not accurately represent the lenses’ ability to block UV rays.
Always check the label on your lenses to see what level, if any, of UV protection they offer. Also, remember that dark sunglasses without UV protection will cause more damage to your eyes than not wearing sunglasses at all. Darker tints can cause the pupil to dilate, letting more UV rays into the inner part of the eye.