Bobster Road Master Global Vision photochromic padded riding glass Transitions and Spectralite
 

Q.What is a photochromic lens?

A. Photochromic lenses adjust the density of their tint to varying light conditions. During the manufacture of a lens, silver halide crystals are added to the lens. There are billions of these crystals in each lens. When struck by ultraviolet radiation and near visible light, they transform into clusters of light absorbing particles. As these particles block and absorb light, the lens darkens.

Once the lens is removed from direct exposure to ultraviolet light, the silver halide clusters disperse into their natural state and again form into micro-crystals. As this happens the lens lightens. Because the silver halide is trapped inside the lens material, the process can be repeated indefinitely.

A photochromic reaction does not happen with "light switch" speed in a polarized lens. The human eye will not readily detect the change in the lens as it is occurring. It normally takes (on average) one to two minutes for photochromatic lenses to adjust from very low levels of light to very bright and vice versa. Also, the tint change is usually not very dramatic. Photochromatic lenses usually range from 10% light transmission in bright light to 20% light transmission in low light. A difference of 10% transmission is not always noticeable, but over long periods of time, you should notice a significant reduction in eye strain.

To test photochromic properties, cover 1/2 of one lens. A Post-It Note works well. Hold the lens outside (not behind glass) for 30 seconds, then take off the Post-It and you will see a very distinctive line differentiating the tint densities.

Advantages:

Photochromic lenses are more versatile in changing light conditions.
Photochromic lenses are more comfortable as they adjust to varying light conditions.
Shatter resistant due to the structure of the laminated lens.

Disadvantages:

Will not work behind a windshield
May not be dark enough for some riders

Photochromic lenses darken when exposed to short wavelength radiation (300nm - 400nm) or ultra-violet light, rate of darkening and final transmission of the lens (saturation transmission) depends on the ambient temperature. Photochromatics will require conditioning the lens first through several exposures to the sun in order to darken fully. Some Photochromatic lenses never get fully dark and some lenses may never become fully clear, This is due to the range of transition. Generally sunglasses never get fully clear and riding glasses never get fully dark, this is because riders need clear vision at night, coupled with shatterproof protection.

Bobster and Global Vision both make several models of photochromic padded riding glass, Transitions and Spectralite are two common lens names in the prescription eyewear industry. Photochromics can be cool and convenient, but don't expect them to go from clear to pitch Black in a nanosecond.

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