
Here's a little useful information about sun reactive lenses
To call a prescription lens a "React to light" lens is a little misleading. It is actually a lens coating applied to a plastic prescription lens that is sensitive to different uv (ultra violet) light conditions. There are many brands of lenses that can have this type of coating applied.
The coating is sprayed on multiple pairs of prescription lenses at a time, and is highly specialised, requiring grease free lenses and a sterile environment. This is an expensive process, so the process is only undertaken by very specialised and large optical lens suppliers and manufacturers. For perfect results we at Ilkeston Factory Specs by lenses in with these types of coatings. Additional coatings can and usually are added to react to light sensitive lenses like hard and anti glare (resistant) coatings.
Are React-a-light lenses made from glass or plastic ?
In days gone by, React-to-Light type lenses were made from glass, but over the last few years the vast majority of these lenses are now made as a plastic lens with an additional coating.
How do they work ?
A layer of reactive pigment is added to the surface of the prescription lens, which is reactive to ultra violet light and also air temperature. The reaction speed and depth of colour tends to mature and be more reactive over time. New reactive lenses tend to be lighter in colour when not reacted or indoors (than older matured reactive lenses) and don't react as quickly until fully matured. As the lenses get older they react more quickly and can become darker when fully reacted. They tend to retain some colour permanently, even indoors, when they are more mature. These coatings have a lifespan and can stay dark all the time when they are at the end of their life. React-to-light lenses tend to last about two years on average.
Are there different types of React-to-light lenses.
There are a few different manufacturers of this type of lens coating in the UK, but all react-to-light coatings work with the same principle. Most Opticians like Specsavers, Scrivens, Vision Express and most independent Opticians tend to buy in and offer industry standard react-to-light coatings, and there are also a few high end suppliers like Zeiss and Essilor, who offer these coatings and some specialist coatings with there more expensive lens brands. Photo-Fusion and Transition are two of their brands of coating. Specialist coatings are more expensive and can offer polarisation, extra thick (micron) coatings designed to work through windscreens or indoors etc, but these lenses, due to price restrictions, are not generally bought or supplied unless specifically requested, and only account for a small percentage of react-to-light lens sales. All react-to light lenses will change colour depth in different conditions at different rates depending on the conditions and the brand etc and all are subject to uv and temperature limitations.
Do React-to-light lenses go as dark as sunglasses ?
The simple answer is no.
React-to-light lenses are adaptive to different light conditions where as sunglasses stay at the one set depth of colour and never change. Sunglasses are used only as sunglasses and generally not at night or in dull light conditions, so they can be tinted darker than a react-to-light lens can reach or be practically used. For glasses to wear in all light conditions, choose react-to-light lenses. For pure depth of permanent shade, you'll need full sunglasses lenses.
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