Photo chromatic as the name suggest are lenses that change color from light to dark according to the ultra-violet rays they are exposed to. Photo chromatic lenses are also known as photo grey and photo brown lenses as the name suggest theses lenses are available in Grey and Brown tint.

These lenses can be used indoor for regular use and outdoor as sunglasses. Since the darkness of the lenses depends on the amount of Ultraviolet rays that the lenses are exposed to the lenses adjusts it darkness accordingly for better vision. These lenses are widely used with prescription eyeglasses as this works as sunglasses and as normal prescription eyeglasses.

The main ingredient that causes the lenses to turn its color is Silver Halide and it is mixed evenly throughout the lenses. This causes the lenses to change color when it is exposed to ultraviolet rays. 

There are few disadvantages of these lenses. One of which is theses lenses will not change color if you are driving as the windshield filters the UV rays. The other is if your prescription is strong then the thicker part of the lenses will be darker than the thinner part. Also if there is a different in prescription between the two eyes then the lenses with the stronger prescription will be slightly darker than the weaker ones.

If you are looking for lenses that change color behind the wind shield then you should opt for Drive wear from transitions. These lenses are more expensive then the conventional photo chromatic lenses but theses lenses will definitely change color if you are behind the windshield of your vehicle.

Initially the lenses were available in prescription eyeglasses only but with technology the lenses now comes in plastic, polycarbonate and hi-index. 

Its time to protect your eyes from Cataracts and macular degenerations upgrade your prescription eyeglasses to photo chromatic lenses which will block harmful UVA and UVB rays.