Photochromic lenses are eyeglass lenses that are clear (or nearly clear) indoors and darken automatically when exposed to sunlight. Other terms sometimes used for photochromic lenses include “light-adaptive lenses” and “variable tint lenses.”

The most popular brand of photochromic lenses sold in the United States Are Transitions Lenses (Transitions Optical). Because of this, some people — including some eye care practitioners — refer to photochromic lenses as “transitions lenses” or “transition lenses.” But there are other brands of photochromic lenses available as well.

The molecules responsible for causing photochromic lenses to darken are activated by the sun’s ultraviolet radiation. Because UV rays penetrate clouds, photochromic lenses will darken on overcast days as well as sunny days.

Photochromic lenses typically will not darken inside a vehicle because the windshield glass blocks most UV rays. Recent advancements in technology allow some photochromic lenses to activate with both UV and visible light, providing some darkening behind the windshield. Ask your optician for details.

Photochromic lenses are available in nearly all lens materials and designs, including high-index lenses, bifocals and progressive lenses. An added benefit of photochromic lenses is that they shield your eyes from 100 percent of the sun’s harmful UVA and UVB rays.

Because a person’s lifetime exposure to sunlight and UV radiation has been associated with cataracts later in life, it’s a good idea to consider photochromic lenses for children’s eyewear as well as for eyeglasses for adults. Polycarbonate is the safest lens material for kids, providing up to 10 times the impact resistance of other lens materials.

Adding anti-reflective coating to photochromic lenses enhances their performance even further. AR coating allows more light to pass through photochromic lenses for sharper vision in low-light conditions (such as driving at night), and eliminates bothersome reflections of sunlight and other light from the backside of the lenses in bright conditions.

Though photochromic lenses cost more than clear eyeglass lenses, they offer the convenience of reducing the need to carry a pair of prescription sunglasses with you everywhere you go.

Photochromic Sunglasses :

Photochromic sunglasses are primarily for outdoor wear. They are not as clear indoors as other photochromic lenses, but they provide extra comfort in bright sunlight and behind the wheel.

Light-adaptive lenses can be placed in just about any fashion frame. They’re convenient for everyday use as well as travel.

Transitions Drive wear (Transitions Optical and Younger Optics) — These polarized adaptive lenses are designed specifically for the driving task. They adapt to changing light conditions when worn inside a vehicle, enhance contrast, and improve visual performance for driving, according to Transitions Optical.

Transitions Optical also has incorporated the company’s photochromic technology into a line of adaptive sunglasses, motorcycle and bike helmet shields and snow goggles. These products enhance visual performance during outdoor activities by providing comfort in changing light conditions, enhancing contrast and offering the convenience of not having to switch products as light changes, according to the company.

Transitions Optical’s photochromic technology is available in products from leading brands like Bell Helmets, Shoei, Oakley, Nike and Dragon Alliance in a variety of tint and color options, including clear to dark lenses, dark to darker lenses, and clear to dark helmet shields. Also, the photochromic performance of products made for snowboarding and other winter activities is optimized for cold temperatures, according to the company.

Medical Applications Of Photochromic Lenses :

In addition to adjusting automatically to different lighting conditions, some photochromic lenses also have medical applications.

Corning’s CPF family of glass photochromic lenses has specially selected red colors. These lenses sometimes are used to enhance the vision of patients who have various eye pathologies, including macular degeneration. Doctors who specialize in low vision are familiar with these lenses and can determine if they will be effective for specific vision problems.

Non-Photochromic Tinted Lenses :

Alternatives to photochromic lenses for improving visual comfort are lenses with tints that remain constant at all times.

Tints of virtually any color can be applied to eyeglass lenses. Lighter, fashion tints are used primarily for cosmetic purposes to enhance a wearer’s looks. Darker tints allow the wearer to use the lenses as sunglasses.

Color can be added to a lens as a solid tint, where the entire lens has the same color density, or as a gradient tint, where the color density is darkest at the top of the lens and gradually fades to clear or nearly clear at the bottom.

Different colors can be applied to lenses for different purposes:

Yellow often is added to a lens to enhance contrast, especially in overcast conditions, making it a popular tint for hunters who desire “shooting glasses.”

Green, or its cousin G-15 (the classic color of lenses in Ray-Ban sunglasses), is sometimes used as a sunglass tint, though brown and gray are the most popular sun shades.

Red is a bold fashion color and also is popular among people who enjoy seeing the world through “rose-colored glasses.