How Do Sunglasses Work?
There are four things that a good pair of sunglasses should do for you:
- Sunglasses provide protection from ultraviolet rays in sunlight. Ultraviolet (UV) light damages the cornea and the retina. Good sunglasses can eliminate UV rays completely.
- Sunglasses provide protection from intense light. When the eye receives too much light, it naturally closes the iris. Once it has closed the iris as far as it can, the next step is squinting. If there is still too much light, as there can be when sunlight is reflecting off of snow, the result is damage to the retina. Good sunglasses can block light entering the eyes by as much as 97 percent to avoid damage.
- Sunglasses provide protection from glare. Certain surfaces, such as water, can reflect a great deal of light, and the bright spots can be distracting or can hide objects. Good sunglasses can completely eliminate this kind of glare using polarization (we’ll discuss polarization later).
- Sunglasses eliminate specific frequencies of light. Certain frequencies of light can blur vision, and others can enhance contrast. Choosing the right color for your sunglasses lets them work better in specific situations.
What to Look For
When you’re buying sunglasses you should make sure you get a pair that will help your eyes. A good pair should provide protection from UV light, protection from intense light, protection from glare, and eliminate specific frequencies of light. Some of the technology used to do this are: tinting, polarization, photochromic lenses, scratch resistant coating, anti-reflective coatings, and UV coatings.
- If the sun doesn’t bother my eyes, do I still need to wear sunglasses?
Yes. The sun has damaging UV rays that can cause photokeratitis, pingueculae and permanent retinal damage.
What exactly are UV rays?
Good sunglasses are extremely effective “light conditioners.” They modify incoming light to match it to your eyes.A light wave consists of electromagnetic energy.The amount of energy in a light wave is proportionally related to its wavelength: shorter wavelengths have higher energy. Of visible light, violet has the most energy and red the least. Just above the visible light spectrum is ultraviolet (UV) light, and it turns out that natural sunlight is rich in UV light. Because of its high energy, UV light can damage both your cornea and your retina.
What is Glare?
The brightness or intensity of light is measured in lumens. When the brightness of the direct or reflected light gets to about 4,000 lumens, our eyes begin to have difficulty absorbing the light. What we see when we try to look at these brighter areas are flashes of white — this is glare. To reduce the discomfort caused by the amount of light entering our eyes, we squint. Once you get to around 10,000 lumens, your eyes are so bombarded that they begin to completely block out the light. Prolonged exposure to light of such intensity can cause damage resulting in temporary or even permanent blindness.
Visible light is light that can be perceived by the human eye. When you look at the visible light of the sun, it appears to be colorless, which we call white. It is made up of many color frequencies. The combination of every color in the visible spectrum produces a light that is colorless, or white.
When do UV rays affect my eyes?
Most people think that they’re at risk only when they’re outside on a sunny day, but UV light can go right through clouds, so it doesn’t matter if the sky is overcast. The sun’s rays are strongest between 10 am and 2 pm.
Glare and reflections can give you trouble, so have your sunglasses ready if you’ll be around snow, water or sand, or if you’ll be driving (windshields are a big glare source).
Can certain medical problems increase my risk for damage from UV rays?
Yes. People with cataracts (or who have had cataract surgery), macular degeneration and retinal dystrophies should be extra careful. Read more about these conditions in our Eye Problems and Diseases section.
What are my options to prevent UV damage to my eyes?
You must wear sunglasses to prevent damage to your eyes. While some contact lenses provide UV protection, they don’t cover your whole eye, so you still need sunglasses.
Look for sunglasses that protect you from 99 to 100 percent of both UVA and UVB light. This includes those labeled as “UV 400,” which blocks all light rays with wavelengths up to 400 nanometers. (This covers all of UVA and UVB rays.)
Also, you may want to consider wraparound sunglasses to prevent harmful UV rays from entering around the frame.
What are the different kinds of lenses that are available?
With so many lenses available, it’s a good idea to ask a professional optician for help when choosing sunglasses. Different tints can help you see better in certain conditions, and a knowledgeable optician can help you choose sunglass tints that are best suited for your needs.
- Blue-blockers block blue light and usually have amber lenses. Some evidence indicates blue light is harmful, and could increase risk of eye damage from diseases such as macular degeneration. These lenses are popular among skiers, hunters, boaters and pilots who use them to heighten contrast.
- Mirror-coated lenses limit the amount of light entering your eyes, so you’re more comfortable.
- Mirror coatings (also called flash coatings) are highly reflective coatings applied to the front surface of sunglass lenses to reduce the amount of light entering the eye. This makes them especially beneficial for activities in very bright conditions, such as snow skiing on a sunny day.
- The mirrored sunglasses associated with state troopers are one example of a flash coating. The technology has advanced, however, so that today’s choices in mirror coatings include all colors of the rainbow, as well as silver, gold and copper metallic colors. Hot pink, blue — almost any color is available.
Choosing the color of a mirror coating is a purely cosmetic decision. The color of the mirror coating you choose does not influence your color perception — it’s the color of the tinted lens under the coating that determines how mirrored sunglasses affect your color vision.
- Gradient lenses are tinted from the top down, so that the top of the lens is darkest. These lenses are good for driving, because they shield your eyes from overhead sunlight and allow more light through the bottom half of the lens so you can see your dashboard clearly.
- Double gradient refers to lenses that are also tinted from the bottom up: The top and bottom are darkest and the middle has a lighter tint. Double gradient lenses are a great choice if you want sunglasses that aren’t too dark, but shield your eyes well against bright overhead sunlight and light reflecting off sand, water and other reflective surfaces at your feet.
- Photochromic lenses adjust their level of darkness based on the amount of UV light they’re exposed to. Read more about photochromic lenses.
Which lens color is the best?
Lens color is a personal choice and doesn’t affect how well sunglass lenses protect your eyes from UV light. Gray and brown are popular because they distort color perception the least.
Athletes often prefer other tints for their contrast-enhancing properties. For example, yellow lenses are popular with skiers and target shooters because they work well in low light, reduce haze and increase contrast for a sharper image.
What is the best shape for an Oval face shape like me?
Do I still need those “UV Protective” sunglasses if my lenses are real dark?
Yes! Most people believe that the darkness of the lens is what protects their eyes. The degree of darkness has no effect on UV rays. For adequate protection, you need to buy sunglasses that indicate they block 100 percent of the sun’s UV rays.
Are the more expensive sunglasses of better quality?
Not necessarily. While expensive sunglasses usually are high quality, you can also get a good pair for under $20 if you’re a careful shopper. Just make sure to check that the lenses provide adequate protection from UV light and are free of distortions.
You can also take them to your eye care professional to have the lenses metered to determine the amount of UV that passes through the lenses. That way you can be sure you are getting the most from your sunglasses.
See the difference between Regular with Polarized Sunglasses
I wear glasses. What options are available to me?
You can buy prescription sunglasses or glasses with photochromic lenses (which change from clear to dark) from your eye care practitioner. Clip-ons may be a less expensive option, and can be bought at the same time as your regular eyeglasses to perfectly match the frames.
Some eyeglass frames include sun lenses that magnetically attach to the frame. This gives you the convenience of clip-on sunglasses with less risk of scratching your prescription lenses.
Do those sunglasses for specific sports really make a difference?
Yes. Sports eyewear in general tends to be safer than regular sunglasses because the lenses and frames are made of special materials that are unlikely to shatter if struck and can give you the benefits of both sunglasses and protective eyewear.
Also, certain lens colors in performance sunglasses can enhance your vision for certain sports; brown, for example, is popular with golfers because it provides nice contrast on those very green golf courses.