Photochromic Technology Enhances Vision
Photochromic lenses automatically adjust to changing light conditions. These advanced lenses darken in sunlight and clear up indoors, eliminating the need for separate sunglasses.
Chemical Reaction Creates Darkening
The magic happens through two main technologies. Glass lenses use silver halides that react with UV light, while plastic lenses employ organic molecules that change shape when exposed to sunlight. Both processes reverse in low light conditions.
Transition Speed Varies
The lenses darken quickly – reaching substantial tint within one minute and maximum darkness in 15 minutes. Clearing takes slightly longer, with noticeable lightening in 2 minutes and full clarity in about 15 minutes.
Temperature Affects Performance
Heat impacts how dark the lenses get. In hot weather, they won’t achieve maximum darkness due to thermal dependency. Cold conditions create deeper tinting but slower clearing times when moving indoors.
Real-World Benefits Show
I’ve found these lenses particularly useful for motorcycle riding, where light conditions change frequently. The automatic adjustment eliminates the need to swap shields or wear sunglasses under your visor.
Limitations Exist
Even at their clearest, the lenses absorb about 20% of ambient light. This slight tint helps reduce eye strain but means they’re not completely clear like standard lenses.
The technology continues to evolve since its development by Corning Glass Works in the 1960s. Modern versions offer improved performance while maintaining the convenience of automatic light adaptation.
Citations:
https://en.wikipedia.org/wiki/Photochromic_lens
A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation. In the absence of activating light, the lenses return to their clear state. Photochromic lenses may be made of polycarbonate, or another plastic. Glass lenses use visible light to darken. They are principally used in glasses that are dark in bright sunlight, but clear, or more rarely, lightly tinted in low ambient light conditions. They darken significantly within about a minute of exposure to bright light and take somewhat longer to clear. A range of clear and dark transmittances is available.
In one sort of technology, molecules of silver chloride or another silver halide are embedded in photochromic lenses. They are transparent to visible light without significant ultraviolet component, which is normal for artificial lighting. In another sort of technology, organic photochromic molecules, when exposed to ultraviolet (UV) rays as in direct sunlight, undergo a chemical process that causes them to change shape and absorb a significant percentage of the visible light, i.e., they darken. These processes are reversible; once the lens is removed from strong sources of UV rays the photochromic compounds return to their transparent state.
