Many of us do know know what it is called. The two in one glasses for all kind of occasion. You go inside the house, it becomes a glass and also protect your eyes in the sun by getting darn when you are i the sun.
What are they?
Photochromic Lens are optical lenses that darken on the exposure to some type of light with enough intensity mostly UV (ultraviolet) radiation.
They were developed by at Corning Glass works inc. by Roger Araujo in the 1960’s.
What are they made of?
They can be made of glass, polycarbonate and plastic.
Where are they used?
This type of lens are highly popular in hot regions, where people expose to more sunlight. These glasses are darn in the bright sunlight but is clear in low lights.
This glass version of this lenses achieve their properties through the insertion of microcrystalline silver halides in glass substrate. Plastic Photochromotic lenses uses organic photochromic molecules to gain reversible darkening effect.
They are useful and different because the lenses turn dark when you expose to uv lights and it protect your eyes from harmful rays. It do not get dark on exposure to other lights so it can be worn as 2 in 1.
You can also log into www.eyedo.in for variations.