Photochrome - what is it?
PHOTOCHROME - what is it?
Photochrome (or transition lens) is an intellectual lens which is sensitive to the illumination level. This lens is transparent indoors but sunlight makes it darker depending on the level of UV radiation. If you enter a dark underground walkway or subway your lens immediately becomes lighter. It’s very convenient especially for those who don’t like to change glasses frequently. One and the same your favourite frame can be an office and a sunprotective one. However, it is not easy to select a universal frame, because dark lens glasses can look smaller and more aggressive. Vice versa, brilliantly looking sunprotective glasses with light lenses can lose all their charm. That is why you should be very careful while choosing a frame for photochrome lenses. It’s a good idea to ask an experienced adviser for help. He/she considers both versions at once due to the work experience.
What types of photochrome are there?
Manufacturers usually suggest only two colors. They are grey and brown. In reality there are different shades of colors which often depend on the shipment. That is why it is a good idea to look at the samles. In the course of work the shade and the level of darkening can change. So, it isn’t desirable to fix one lens. Blue, green, vinous and purple shades are produced on order , but they are much more expensive than ordinary colors.
PHOTOCHROME ACCORDING TO MANUFACTURING TECHNOLOGY
The whole lens contains an active photochrome pigment. On the one side this version has the longest lifespan, but on the other side the color and the level of darkening depend greatly on the lens thickness. A thinner center of a minus lens can look very light against the background of the edges and lenses with different diopters darken at different speed. Such photochromes lighten slowly and the translucence level constantly decreases in use. This technology is mostly connected with archaic mineral lenses, but can often be seen in ready-made glasses.
Only the lens surface is saturated with an active photochrome pigment. Due to this fact we achieve even color all over the lens and the speed of darkening slightly depends on diopters. This is the most popular technology nowadays. But take into consideration the fact that photochrome pigment becomes colorless in use. After several thousands cycles of darkening-translucence lenses stop working. That is why, it’s not woth saving money if you are often in the open air. The difference in prices of various manufacturers of photochrome lenses is determined by their lifespan. Most low-budget brands don’t serve till the end of their warranty period and can lose the ability to darken even in a couple of months. So, choose proven manufacturers and don’t try to save money.
A photochrome pigment contains a thin film coating on the surface of a lens. Due to this fact lenses of any diopters darken or lighten in the same way. The fastest working technology nowadays has, besides high prices, one more drawback - the surface darkens in the sunlight but the edges of the lens remain light.
It is essential that photochrome lenses are not very good with withstanding heating and pressure. It’s not a good idea to put your glasses on your car’s dashboard and the spectacle-case shouldn’t be too narrow. Otherwise a lens can get covered with a slightly seen but very disturbing net of microfractures.
PHOTOCHROME’S CHARACTERISTICS
What is the level of photochrome’s darkness in the sun? That is the most essential question. In practice, this characteristic is dynamic and depends on a lot of factors, mainly on the ultraviolet level (not luminosity) and on the air temperature. Only darkening in standard conditions is denoted in characteristics (at standard temperature under a standard radiator). As a result, all photochrome lenses have nearly the same specified levels of darkening/translucence to meet all-Union State Standards and EU standards requirements.
This characteristic is the most important one, if you want to use photochrome lenses as sunprotective ones in summer. The higher the temperature, the less is the level of photochrome lens’ darkening. In practice, it is important to know to what temperature photochrome maintains its stated advertising characteristics. Most budget-choice brands start darken badly at +25°C. It’s quite suitable for town conditions. But if you are going to the beach, it’s better to choose film transition which maintains darkening characteristics up to +40°C. But bear in mind the perverse effect - if you like skiing on a sunny frosty day, photochrome can darken up to full non-transparency.
We have conducted a lot of experiments with different lens brands and we are confident that all photochromes (if the level of ultraviolet radiation is sufficient) attain the highest stated level of darkening at the same speed (about 30 seconds). The translucence speed is also the same with different manufacturers (2 minutes until essential translucence and 30 minutes until full translucence). But the level of maximum darkening and maximum transparence of different brands varies greatly. Choose the characteristics which are suitable namely for you.
How to choose photochrome?
Modern optics market offers a great number of versions of photochrome lenses, but not all of them are budget-choice brands. That is why the first thing you should do is to decide what is more important for you, the outside appearance of the frame or its functionality.
If you mostly work indoors, choose the most transparent transition-7. If you need a universal version, study all offers, get to know about the peculiarities of various brands, pay attention to the working lifespan. If you need big diopters, choose from aspherical high-index versions. If you want glasses for a hot southern beach, your choice is only transition, the one which darkens at high temperature.If you work a lot on the computer, choose brown photochrome with a high level of protection against the blue spectrum of the monitor. If you drive a car, take into account that the windscreen slows down ultraviolet. Only a specially worked out extractive for drivers can darken from visible-light spectrum in your car. The extractive darkens while driving but can also darken from the bright light of some energy-saving lamps.
Besides the above mentioned, attention should be paid to the color of the photochrome lens because darkening often happens during the transitional state when the color of your eyes and skin can either match or not the tone of your lens. So, choosing a photochrome lens it’s a good idea to have a look at a darkened by a UV lamp sample, put it on your skin and make sure that the purchase will be perfect for you.
In any case, adapting themselves to the illumination level lenses will give you extraordinary visual comfort.
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