How Sunglasses Protect Your Eyes
Sunglasses protect your eyes from dangerous light. The technologies and coatings for sunglasses that make this possible are as fascinating as they are varied. When you go to buy sunglasses, we advise you to look for features that provide the protection you require for the purpose you plan to use your glasses.
Tinting
Sunglasses are tinted various colors. The color tint determines which colors of light the lenses absorb. The most common method for tinting involves immersing the lenses in a special material, so that the tint is absorbed into the plastic lens.
One goal for tinting is to reduce the amount of blue light, which can create glare (known as blue haze). Here’s what different color tints will do:
- Purple and rose tints provide excellent contrast when the background is green or blue.
- Green tints reduce glare and offer high contrast. They filter some blue light.
- Amber and brown tints reduce glare and absorb high frequency colors. They do a good job absorbing blue light.
- Yellow and gold tints almost eliminate blue light. They make things look bright and clear, but they can distort colors. Yellow and gold tinted glasses are best in the snow.
- Gray tints reduce brightness, minimally distorting color, and protect against glare. They’re a good choice for driving.
Polarization
Light is polarized when vibrations from light waves are aligned in a direction. Water and highways are the most common sources of glare. Light striking these surfaces is reflected. The light then becomes polarized as it matches the surface’s angle. Polarized lenses are fixed at an angle to let in vertically polarized light, reducing glare.
Many sunglasses are advertised as polarized, but aren’t. How can you tell? Find a reflective surface and hold your sunglasses so that you can see the surface through one lens. Rotate the glasses to see if the glare increases or decreases. If the glare decreases, then you know your sunglasses are polarized.
Photochomic Sunglasses
Photochromic sunglasses darken when they’re exposed to sunlight thanks to a chemical reaction between the lenses and UV radiation. Molecules in photochromic lenses are transparent to visible light but change shape when exposed to UV light, absorbing visible light and causing the lenses to grow darker. Indoors, the reaction reverses. Photochromic sunglasses only darken when exposed to UV light; in your car, for instance, they won’t darken because the windshield blocks most UV light. Generally, most photochromic lenses have some tint.
Mirroring
Reflective coatings, called a half-silvered surface, give sunglasses a mirrored look. The coating reflects about half the light that strikes it. Mirror coatings sometimes change shades from top to bottom, adding protection from light coming from above, but letting more light come straight through.
Scratch-Resistant Coating
This should be self-explanatory. Plastics are not naturally scratch resistant, so manufacturers have developed optically clean, hard films to place on the lens’ surface. Glass is naturally scratch resistant.
Anti-Reflective Coating
Anti-reflective coating reduces back-glare, the light that hits the back of the lenses and bounces into the eyes. It’s made of a hard, thin film, which is layered on the lens.
Ultraviolet Coating
A UV coating can eliminate UV radiation. UV light can be absorbed by your retina and lead to cataracts. Overexposure to UV radiation can create a kind of sunburn on your retina, called photokeratitis, or even cancer. A good pair of sunglasses should filter out 99 percent of both UV-A and UV-B, the two categories of UV light.
These Solis Eyegear glasses are highly reflective sunglasses.
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