We Know: All About Photo Gray Lenses
What Are Photo Gray Lenses?
Photo gray lenses darken automatically upon exposure to sunlight or even bright indoor light, and lighten when you go into darker areas. Photo gray lenses do not always filter damaging UV light unless they are specially treated to do so. However, they are an excellent choice when you move from dark to light areas frequently, or if you have certain eye problems.
Photo gray lenses are also called photochromic lenses or variable-tint lenses. And you're not limited to gray colors; some photochromic lenses come in brown as well.
How Do Photo Gray Lenses Work?
In the glass or plastic used to make the glasses lens, silver halide is mixed in evenly. This substance is sensitive to ultraviolet light, and will darken when exposed to it. The drawback of this method is that thicker parts of a lens will turn darker, and if you have differing prescriptions for your eyes, one will look darker than the other. If you don't like this idea, you might want to use two pairs of glasses -- one regular prescription pair and a second prescription pair with sunglass tinting.
What Are Photo Gray lenses Used For?
Besides being a handy way to not lose your sunglasses, photo gray lenses are used for certain medical conditions. Patients who have a low vision ocular pathology sometimes need glasses with photosensitive lenses in the red family. People who have low-level light sensitivity also may find photo gray lenses in the red family to be helpful.
You can also get pre-tinted photo gray lenses for driving. The color in photo gray lenses reacts to UV sunlight, and in your car the windshield may cut out much of the UV rays, not leaving enough to activate your glasses. In this situation, you should wear glasses with a tint in the car for sunny-day driving, but with photo gray treatment so that they'll change to a darker color when you're back in sunlight.
Regardless of why you're using photo gray lenses, be certain to get a pair that provides adequate UV protection when you wear them.