Photochromic lenses, or chameleon lenses, have a variable light transmission. This means that they change transparency depending on the lighting. When they get ultraviolet rays, the lenses get dark, but when you go inside, they’re colorless again, like regular glasses. In this article we will answer questions about how photochromic glasses work, what their pros and cons are.
Photochromic blue light blocking glasses work principle.
The principle of operation of photochromic glasses is quite simple: thanks to the special material of their lenses, they can be darkened by exposure to ultraviolet light. The fact is that ultraviolet changes the spatial structure of the molecules that make up the lenses, the brightness of light decreases, and photochromic glasses actually turn into sunglasses with the level of obscuration corresponding to the illumination.
Temperature conditions are important: in hot weather, photochrome glasses cannot be darkened to their maximum value, whereas in medium and cool temperatures the speed and degree of blackout is higher. Therefore, it is better to buy sunglasses with diopters for your holidays in hot countries, but in the conditions of the city even not completely darkened photochromes will protect your eyes from bright light. Remember that «chameleons» react to ultraviolet rays, so they can change color in cloudy weather.
How are photochromic lenses made?
As a rule, photochromic lenses change their colors to the most popular and convenient colors in solar optics — brown, grey or green. These colors are the most comfortable for the eyes and provide the most natural color transmission.
Some manufacturers offer a wider palette for photochrome glasses, such as sapphire and amethyst lens-«chameleons».
Today there are several technologies of lens production with variable light transmission.
Photochrome coating. A thin layer of photochrome particles is applied to the surface of the lens to obscure it. This method is currently considered obsolete because the degree of light absorption is not high enough and the time for obscuration and illumination is long.
Introducing photochrome agents into the material. They imprint already finished lenses. The most famous brand is Transitions.
It’s a volumetric-distributed technology. The point is that photochrome molecules are evenly distributed in the lens material when they’re made. SunSensors produces such optical products.
Features of photochromic lenses.
Now that we’ve worked out what photochrome lenses mean, let’s talk about their peculiarities. At first glance, it seems that such optical products are the best choice for any human being. They provide comfort both indoors and outdoors, with no effort to see clearly.
However, photochrome glasses have their own nuances of use.
— The lenses don’t get dark and light immediately.
This is one of the main indicators that you are advised to pay attention to when ordering glasses. The average reaction time for photochrome cells is between 30 seconds and 5 minutes. It should be noted that changing the color of the lens starts immediately, i.e. you will not find yourself in a situation where the glasses remain completely black in the room. The smooth change of light transmission capacity is comfortable for the eyes, so customers do not usually complain about this feature.
— Lenses can get dark and light unevenly.
There are two reasons why they do this. In articles that are produced using the volumetric method, photochrome molecules are introduced into the material at random, and in some places they may be smaller than in others. The second reason is the different thickness of lenses in the center and periphery of myopia and hypermetropia. If you darken, you’ll be left with areas of a different color.
— The degree and speed of darkening depends on the surrounding temperature. The reaction is faster in warm weather and slower in cold. At temperatures above 30 C, lenses darken not completely, but by 90-95%, which can cause discomfort to the inhabitants of the southern regions. In the cold, on the other hand, the glasses give off their maximum, which is not always convenient with variable clouds or a walk in the forest with constantly changing lighting.
— Photochromic lenses have a life of 2 to 5 years. Gradually the service life is produced under the influence of UV radiation and the light absorption indices deteriorate. It should be noted, however, that first, the manufacturers are constantly working on extending the life of lenses, and second, ophthalmologists recommend that people with refractive impairments undergo eye checks and change their glasses every 2-3 years if necessary.
Benefits of photochromic lenses. Pros and cons.
Let’s start with the advantages of chameleon glasses:
— «Two in one» — glasses with photochromic lenses make life much easier for people in need of correction of their sight. No longer need to squint from the sun or wear sunglasses to the detriment of good visibility, chameleon glasses will provide both necessary correction and protection against bright sunlight;
— Care for people with eye diseases and photosensitivity — photochrome optics relieve the condition of people who suffer from diseases that cause increased sensitivity to light. Glasses that adapt quickly to changes in lighting effectively protect the eyes from pain and discomfort;
— Special lenses for drivers — glasses with such lenses react not only to ultraviolet radiation, but also to visible light, making lenses darker even if not directly exposed to the sun. Such glasses can also block the glare if additionally equipped with a polarization filter.
The shortcomings of this optics are less:
— High cost — Sunglasses adapted for lighting cost more than normal corrective or sunny optics. However, the market offers a wide range of lenses in different price segments, which allows the selection of photochromic glasses for almost any budget;
— Limited range of colors — Unlike sunproof and tinted optics, photochrome glasses have a small palette of possible colors.
Photochromic lenses are a lifesaver for people in need of visual correction. Glasses with such lenses remain light indoors and darken by sunlight. ‘Chameleons’ are also recommended to people who suffer from eye diseases provoking light fear.