Sunlight is called white light, and is, as just noted, composed of all the colors of the rainbow. When sunlight falls upon a body, a part of the light is absorbed by the body and converted into heat. The rest of the light is reflected to the eye and renders the body visible. If the body reflects all the colors of the rainbow equally, then the body is white. If the molecules of the body absorb certain compound colors of sunlight, then the reflected light is deprived of those particular colors. To illustrate: If blue is absorbed, the light reflected will be deprived of this primary color and the active remaining color which is red will predominate. Thus, the body will appear red.
This theory of light has been used to advantage in protecting the eyes of the workmen engaged in electric and oxy-acetylene welding. When metals are heated to a very high temperature, the eyes of the workman may be damaged by the repeated flashes of brilliant light from the glowing metals. Very careful experiments show that certain rays in large amounts, such as the ultra-violet rays and the infra-red rays, are harmful. Such rays are present in the working of molten iron or steel, or any incandescent material, where the temperature is 2000° F. or more. Special colored glasses or lenses will neutralize or cut out these dangerous rays.