You know that in Sunglasses Restorer we like to provide information that can be useful, sometimes related to our products, and sometimes not.
This article has a bit of both
We are going to talk about
We are going to explain you:
We are going to explain you:
- Scientifically definition of photochromism
- Advantages and disadvantages of photochromic lenses
- Usages of Photochromic lenses
Is it enough for you?
First let’s define scientifically what photochromic lenses are:
Photochromism is a reversible light-induced change between two states (A and B) of a molecule with different light absorption spectrums.
LIGHT and CHANGE … just keep these two words in mind.
Let’s create a more understandable definition.
Photochromic lenses are those that turn dark when sunlight (or ultraviolet) impinges on them, and become clear in the absence of such sunlight.
Now it seems clearer, right?
Photochromic lenses are those that change color (darken) if the sun shines in our face, and when we enter into a closed place, become clear.
They have several advantages and disadvantages.
Photochromic lenses advantages
-They are useful when we go shopping for the day: we enter and exit stores continuously, but it´s inconvenient to put on and remove our glasses from our faces.
-When we ride bikes and our journey goes through different sites with shadows and light; on days with sunny spells where you often don’t know whether put or take oof your glasses or throw them away when you’re tired of them.
-All Photochromic glasses have protection against UVA / B 100% up to 400 nm. That is, they offer protection from damaging rays of the sun for eye health.
If we go the beach and are under an umbrella, sunlight still reaches to our eyes (ultraviolet rays).
If, for example we need reading glasses, some photochromic lenses protect us from harmful sunlight.
Inconveniences of Photochromic lenses
– The photochromic effect ends up losing its effectiveness and lenses take on a greyish or yellowish hue.
-They don´t work for extreme sunlight situations(snow, water sports, fishing, etc)
-They don´t activate inside a car (as explained below)
-They’re more expensive than conventional lenses
Ok, here´s the deal
We can talk about two types of photochromic lenses.
Photochromic Lenses manufactured en masse: During the manufacturing process, the photochromic material is incorporated into the body of the lens itself. There is a lot of the photochromic material inside the glass. This has the advantage of much faster activation: the glass darkens much sooner.
Photochromic Lenses with a surface film: when the lens is semi-finished, a thin photochromic sheet is added on the outer side of the lens. Then this coated film is hardened by a treatment which does not come off easily. This makes the lens much cheaper to manufacture, but the effect of color change is much less effective.
What is the composition of Photochromic lenses?
Photochromic lenses for sunglasses, in most cases, are made of polycarbonate.
The photochromic surface treatment is predominant in this type of glasses.
Changing colour materials are often composed of chlorine alloys, silver and copper. It took years of research, until it was found that these compounds were reactive to light and the absence of it.
Each manufacturer determines its final components.
What are they used for?
As mentioned, photochromatic sunglasses are ideal for sports with continuous changing light conditions. The most representative example is the Mountain Bike (MTB). For triathletes who practice IronMan (changes in light from morning to night) and for golf players (the greens are very variable in light conditions), they are a highly recommended option.
So we said before: for sports such as skiing or water sports where the incidence of the sun is extreme, they are not recommended. Ultraviolet radiation is very high, and polarized lenses are recommended in these situations.
Well, that´s all. Did you like it?
Do you now know what a photochromic lens really is?
We really hope so, if not this article would be useless. Please, leave us a comment below. Or maybe do you prefer the Wikipedia definition of photochromism, but it´s very similar to the one we wrote at first.
We have photochromic and polarized lenses. Which one do you choose?
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See you soon.