Photochromic Lenses
Photochromic Lens Technology

Technical Differences
Other than the index of refraction, which relates to thinness of the lens; and specific gravity, which relates to the weight of the lens, the primary difference between surface and in-mass technology relates to how the lenses perform over time. �

Although the leading manufacturers of both plastic photochromic technologies state that the performance of their lenses will outlast the lifetime of an average prescription � considered to be two years or less � lab testing indicates that in-mass plastic lenses last significantly longer. Here�s why. All plastic photochromic lenses will gradually lose their darkening and lightening ability due to UV exposure. This is due to the organic chemistry inherent in plastic photochromic lenses, which degrades in the presence of oxygen and radiation.

As UV degrades the photochromic dyes in the imbibed technology lens, there are simply fewer dyes to step up to replace those that have faded away, which also impacts the consistency of the color over time. When UV degrades the exposed or activated photochromic molecules of in-mass lenses, other molecules step up to replace those lost. Therefore, you have a longer-lasting, more consistent color lens.

Photochromic Lens Colors

Regardless of use, most consumers in North America still prefer gray, while brown is the preferred color in Europe. To satisfy worldwide demand, photochromic lenses are now produced in both gray and brown. But photochromic lenses also are available in a variety of colors. Recently, two new lens brands were announced: Splitz� is produced by Transitions. Splitz lenses change to different colors outdoors using their standard imbibed technology. Rose changes to purple, blue to green and yellow to orange when exposed to sunlight.

Invicta Vision produces a lens called Solera using a coating technology. Solera lenses are made in six colors. The colors don�t change but simply become a darker shade when exposed to sunlight. Neither product claims to be a sunglass and each is aimed instead at a different market than conventional photochromic lenses � they were created for consumers wanting a changeable fashion tint. These companies are betting that the fashion world is ready for functional fashion tints. One thing is certain. The availability of changeable fashion tints is going to broaden the appeal of photochromic lenses.