June 30, 2018

The Basics about Sunglasses

Everyone has heard that they should wear sunglasses when they are outside, and many of us do. But do you know why sunglasses are so important? What factors are important to have in a pair of sunglasses?  This post will give you some basics on sunglasses.

First and foremost, think of sunglasses as sunscreen for your eyes. A good pair of sunglasses will block all forms of ultraviolet (UV) rays from reaching your eyes. UV rays are high-energy wavelength light rays that are just below violet outside the visible spectrum. That is, they are invisible to the human eye. There are three types of UV rays: UVA, UVB, and UVC. UVC rays are, fortunately, blocked by the atmosphere and never reach the earth’s surface. UVB rays are very damaging to the eye, where they can cause sunburns to the cornea (ouch!), early cataracts, or even retinal damage possibly leading to conditions such as macular degeneration. Experts are not certain if UVA rays are harmful to the eyes or not. Regardless, when deciding on a pair of sunglasses, make sure the lenses filter 100% of both UVA and UVB rays. If you are uncertain, a knowledgeable optician should be able to tell you. There are some contact lenses that block UV rays, but since contacts do not cover the entire front of the eye, sunglasses are still needed.

The primary source of UV rays is natural sunlight. Glass blocks UVB rays, and our car windshields are designed to block both UVA and UVB rays. (That is why photochromics, or lenses that transition from clear to dark with exposure to the UV rays from the sun do not work well in a car.) The sunlight is most intense from 10:00 am to 2:00 pm every day, but sunlight and UV rays can reflect off of the ground or any other surface and still get into our eyes at any time during the day. It is also important to remember to wear our sunglasses in the winter, when the sun is lower to the ground, as it makes it even easier for those light rays to reflect off of the ground (or snow) and bounce up into our eyes.

Another important function of sunglasses is to cut glare. We have two tools to allow us to reduce the amount of glare that interferes with our vision: anti-reflective (AR) coating and polarization. Lenses that are polarized are good at reducing glare that is reflecting off of a surface, such as water, a street, or even our car’s windshield. Anti-reflective coating works to reduce glare by not allowing light that hits the inside of our lenses to reflect back into our eyes. (Or by not allowing light that hits the front of our lenses to reflect back out to others, which can be a big problem if photographers who are trying to take your picture and see your eyes behind your glasses.)

What color of sunglasses lenses are best? The answer to this question is completely up to the buyer’s preference. Most people prefer grey because it tends to skew color perception less, or brown to increase contrast and further cut glare. Many people with early cataracts or who play competitive sports prefer yellow for further increased contrast. There is a myth that darker colored sunglasses will block more UV rays.  Remember – UV rays are invisible, so the color of the lens does not matter. Darker lenses will cut more glare and reduce the amount of visible light that gets to your eyes, but has no effect on the amount of UV rays. As an added danger factor, darker glasses cause our pupils to enlarge to allow more light into the eye, which also allows more UV into the eye if the lenses do not protect against UV.

Now you know the basics about sunglasses.  Thank you for reading this post.  Check back in a couple of weeks, when we will go into detail about some advanced options for sunglasses such as mirror coatings and Chemistrie clips.

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