Light	Medium	Dark	Very Dark
Number	1	2	3	4
Letter	A	B	C	D
% Absorbtion (Approximate)	10%	40%	80%	90%
% Transmition (Approximate)	90%	60%	20%	10%

As shown in the table above, the density of color of ophthalmic lenses may be indicated through the use of numbers, letters, or as a percentage of transmission or absorbtion. For example, a light grey tint may be designated as Grey #1, Grey A, Grey 10% or, less commonly, Grey 90% transmission. Occassionally, colors are described simply as light, medium, or dark.

Most CR-39 plastic lenses are manufactured clear, without any tint. Plastic can be tinted virtually any color and it may be changed or modified with relative ease.

There are several methods of achieving tint in glass lenses. Some are manufactured with the color actually in the material itself. Although this used to be more common, certain colors such as Pink #1 and Grey #3 are still available. With this type of colored glass, however, the density of the tint will change with lens thickness, That is, the thicker the lens the darker will be the color. A Grey #3 tint on a +3.50 diopter lens, for example, will be significantly darker than the same designated tint on a +1.00 diopter lens. Another method of achieving color in glass is through the use of a metallic oxide applied to the lens in a vacuum. Vacuum coating permits a wide range of color choices and results in a consistent, even density of color throughout the lens regardless of power. Photochromic lenses, described earlier, are commonly available in glass. The most popular photochromic colors are grey and brown.

Polarized Lenses: Polarized lenses are useful for reducing the amount of glare reflected off surfaces such as water, snow, or metallic surfaces. Reflected light is partially polarized with the major direction of vibration being in the horizontal plane. A polarized lens admits only light vibrating in the vertical plane thus reducing the intensity of glare. A polarized lens contains a filter of polyvinyl alchohol which has be layered or �sandwiched� between the glass or plastic lens material.