Photochromic materials – these change colour according to different lighting conditions and can be used for security markers that can only be seen in ultraviolet light.

Photochromic lenses are optical lenses that darken on exposure to specific types of light most commonly ultraviolet (UV) radiation. These lenses may be made of glass, polycarbonate, or another plastic. They are used in eyeglasses that are dark in bright sunlight, but clear in low light conditions.

Photochromic lenses (also called transitions or ‘reactolights’), darken when exposed to sunlight, or U/V ultraviolet, and return to a clear state when indoors, away from U/V light.

They can take around 30 seconds to fully darken and approx 2 - 5 minutes to return to a clear state.

Welding masks or glasses use the same principle to protect the eyes from the arc when welding. These types of glasses have clear lenses that automatically darken when welding begins or the arc is struck.

Advantages and Benefits of Photochromic Lenses:

• Reduced costs – buying a single pair of dual purpose photochromic glasses can provide vision for both indoors when clear and providing sun protection outside is more cost effective than buying two separate pairs.
• UV protection - Photochromic lenses give full protection against the harmful UV rays of the sun – as direct exposure to sunlight can cause serious eye problems.
• Convenience – no need to switch between 2 pairs of regular glasses to sunglasses.
• Eye Health – reducing exposure to the sun’s UV rays can lower the risk of cataracts or other related problems

Changes in clothing from one colour to another colour are possible mixing photochromic colours with base colours.