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| Photochromic and Color Lenses |
| Photochromic lenses change from light to dark depending on the amount of ultraviolet light they are exposed to. Early photochromics were strictly glass lenses, but today, you can choose from regular plastic, polycarbonate and high-index glass and plastic. Transitions lenses are available for nearly every lens design, refractive index, and prescription. Performance features include advanced variable-tint technology that allows rapid darkening when you go outside (and rapid return to clear when you go in), and 100 percent UV protection. They come in regular, lightweight plastic materials as well as in high-index plastic and polycarbonate. They have a front-surface coating that changes color (to gray or brown) when exposed to ultraviolet light. The changeable coating means that the color darkens evenly regardless of lens prescription or thickness. Transitions also makes a few niche products including for Drivewear, which features a lens that remains dark behind the windshield of a vehicle. As a general rule, photochromic lenses won't darken behind the windshield because the glass blocks out the UV rays that cause the lenses to change color. |
| Lenses with Tints |
| As opposed to the changeable photochromics, another option in colored lenses is a tint, which remains constant at all times. Tints are available on plastic as well as glass lenses and can be had in almost any color of the rainbow. 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.Typically, fashion tints are applied in light pink, brown or gray, while sunglasses are usually gray or brown. A tint can be solid, when the entire lens is the same color, or gradient, which is a gradual fade from dark to light, usually fading from the top down. |
| Other colors can be pplied to lenses for different purposes: |
| Yellow, sometimes referred to as a "blue-blocker" because the color keeps blue light from entering the lens, is often the color of choice for target shooters because it decreases haze and makes objects appear sharper, with more contrast. Green, or its cousin G-15 (the Ray-Ban lens color), is sometimes used as a sunglass, though brown and gray are the most popular sun shades. Red is a very uncomfortable color to look through, though it does have applications for certain ocular pathologies. However, some people enjoy seeing the world through "rose-colored glasses." Tints are applied to plastic lens materials through a process of absorption. The lenses are immersed into a warm color bath, and depending on the length of time they sit in the tank, emerge in varying shades of darkness. A lens that requires only a light tint will go into the bath for just a few minutes, while a lens that is meant to be sunglass-dark will stay in for quite some time. Glass lenses may be manufactured with the color distributed throughout the lens material, or a tint is applied as a coating in a vacuum chamber after fabrication. |
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