How Self-Darkening Eye Glasses Work

"Lenses." [Online image] Available, 4 April 2009.

What Do Self-DarkeningEye Glasses Do?

Self-darkening glasses have transition lenses, which allow them to get darker when exposed to bright light such as the sunlight. Their purpose is to protect the wearer's eyes against the sun without having to pay the extra money of buying a pair of prescription sunglasses. The glasses look normal under average light and turn into temporary sunglasses when outside. Once the wearer goes back inside, or out of the sunlight, the transition lenses go back to their normal, clear state.

How Do Self-Darkening Eye Glasses Work?

Transition lenses are made with photochromic dyes. These dyes react to the sun's UV rays. When the UV rays hit them, the dye reacts and darkens, causing the lenses to darken as well. The darker or lighter the atmosphere is, the more or less the dye reacts. In very bright conditions, the lenses will be extremely dark to protect you from exposing your eyes to too much sunlight. The darker it is, the less the photochromic dye reacts, and the lighter your lenses will be, allowing you to see in dark settings.

Advantages & Disadvantages

There are several things to consider when deciding whether transition lenses are right for you. On the one hand, the glasses are very useful and can save you some money in the long run. You will only need one pair of glasses and won't have to buy a separate pair of prescription sunglasses. It is important to have some form of eye protection against the sun's bright rays. However, transition lenses can cost from $25 to $100 more, added on to the price of your new glasses. The lenses also take about five minutes to transition from dark to light, so entering a dark building after being outside makes it difficult to see. If your car has tinted windows, the glasses may not darkened enough to be effective as sunglasses, causing you to have to buy a second pair of glasses. In the end, it comes down to cost and the personal decision of keeping track of one or two pairs of glasses.