This is a tint that is clear indoors and due to the amount of sunlight darkens like sunglasses outdoors. The Photogray tint is only available in glass lenses. This tint does not work well in a car because most cars have tinted windows.
This tint is available in light weight plastic lenses. Because it darkens when outdoors and lightens indoors it provides both comfort and versatility. The tint also give protection for the UV rays. One should not consider these as sunglasses for driving because they do not tint well in a car because of tinted car windows.
Quality sunglasses filter about 80% of the visible light spectrum and all the UV and infrared rays. The best colors for sunglasses are gray, green or brown. These tints filter more evenly across the visible light spectrum. Quality sun lenses are ground and polished to be free of distortions and imperfections. They are perfectly matched in color and absorption. Standard tinted lenses are available in glass and plastic. Sunglasses are designed for outdoor daytime wear only.
When light strikes a surface like water it becomes scattered and travels in all directions like a child's sparkler. This is what is commonly know as glare. This glare produces eyestrain and discomfort. Standard sunglasses filter out 80% of the light, but cannot block glare. A polarized lens acts like a filter or lattice which allows the useful light traveling from an object to reach the eye, while blocking all the glare caused by the scattered light traveling in many different random directions. Objects then appear sharper and colors are seen more vividly. Therefore, Polarized Sunglasses combine the advantage of "standard sunglasses" with a polarized lens. These lenses are particularly effective around water, snow, sand, or simply driving down the highway. Polarized sun lenses are made by a special process which places an ultra-thin sheet of polarizing film within the lens itself. This protects the film from any damage, allows the lens to be ground to any prescription, and to be tinted.
(article contributed by H. Frank Storey, OD)