In world of sunglasses, Photochromic lenses have recently become very popular. The Photochromic word is combination of two words in which the first “photo” stands for light and the second “chroma” stands for color. So a photo-chromatic lens is such a lens, which changes its color based on its exposure to the light. In case of sunglasses, these lenses change the tint when exposed to light and also in some sort of sunglasses the color of lens changes from drank to light and vice versa when exposed to light. In case of sunglasses, the main purpose of using Photochromic lens is to save the user’s eyes from ultraviolet radiations which will otherwise start damaging the eyes. This sort of sunglasses is usually popular among athletes, hikers and sportsmen who have to travel a lot in sunlight. These lens block the passage of ultraviolet rays by chemical processes and in that way the observer can enjoy working in harmless sunlight.
The working principle of Photochromic lenses is very simple. Initially introduced Photochromic lenses used to be made of silver compounds. These compounds were considered sensitive to sunlight hence when light fell on these lens, the silver compounds undergo chemical processes to turn the color of lens to dark. This helped in preventing some of the UV rays from passing through the glass. Now a day the special type of Photochromic lenses are made which contain polycarbonate or plastics instead of silver compounds. When light falls on these photo-chromatic lenses, the carbon molecules enlarge in size and a sort of rearrangement takes places, this results in building up of a impermeable carbon molecule wall inside the lens through which the UV rays are impossible to pass. Hence these modern photo-chromatic lens sunglasses have proved to be very effective.
It usually takes around a minute or so for lens to react to exposed sunlight and change its color. However some high quality lenses can change the color within 22 to 28 seconds. It depends on the quality of lens. The time to revert from changed state to the original one is usually around 15 minutes. Warmer lens tend to change color more quickly as compared to the cold lenses. This shows the increased efficiency of Photochromic lenses in summer season when sun is at its peak. Also there is a phenomenon names as temperature dependency which saves the lens from damage when exposed abruptly to exceedingly high temperatures by slowing down the thermal changing process.
|How does photochromic lenses work?|
There are a lot of advantages of Photochromic lens sunglasses. A sufficient protection against UV rays can be obtained by using such sunglasses. These glasses are very versatile in nature as these glasses undergo changes according to the changing climate so that in the end a compatible lens is created which can be used according to respective weather. So such sunglasses deprive the user of worry to continuously switch between sunglasses. The UV absorption ratio in modern photo-chromatic lens sunglasses in 100% which provides the protection necessary for saving the eyes from harmful UV rays.