Photochromic lenses are almost as clear as standard plastic when deactivated (approximately 15% absorption), they filter out 100% of UVA and UVB, radiation, whether activated or not.
Recent surveys have shown that more than half of the population would benefit from having greater protection from glare of the sun.
As a variable tint, Photochromic lenses are only as dark as the level of sunlight requires ,they are available in grey and brown tints, these generally tint to approx 75-85% when fully activated. We also offer Pink and Purple Photochromic lenses, these are only a subtle tint of approximately 30% when fully activated.
How Photochromic lenses work
Photochromic & Transitions® lenses contain dye molecules of carbon and the oxygen. Photochromic lenses that are exposed to UV light have this carbon and oxygen bond broken, allowing absorption of light photons, changing the appearance of the lens to the desired colour.
The speed at which these Photochromic dye molecules vibrate is controlled by the temperature, therefore the the amount of UV light influences the initial bond disconnection making them change colour, but it is the temperature that determines how fast these react to that UV light.
Less energy is produced with lower temperatures, making the reaction time slower. A higher temperature generates more energy, yet Photochromic lenses will actually go darker with lower temperatures.
Photochromic lenses do not react behind a windscreen of a car as car manufacturers have built UV protection into windscreens, meaning little or no UV light penetrates the glass.
Often newly purchased Photochromic lenses can take a few exposures to UV light to establish the chemical reaction required to absorb photons of light. Older generation lenses can often have the dye molecules rekindled by placing them in the freezer for 10-15 minutes, but there is limit to how many times this can be achieved.
For more information on Sun lens options click here