The problem of an adequate amount of light presents itself to every manufacturer and city-dweller. With the increasing value of space and the constant crowding of buildings, the natural source of light, the sun, has been shut off in a great many buildings. The result is that artificial illumination in the daytime is a practical necessity. When such artificial sources of light are used in place of sunlight they must meet the needs of the eye and be installed with that aim in view.

Light should not shine directly into the eyes, but directly on the object we wish to see. The paper that gives the greatest amount of diffused reflection is white blotting paper. Dirty paper does not diffuse light as well as a clean, white board. White painted surfaces diffuse light well. Green, red, and brown surfaces have low diffusive values. Color on the walls of rooms and shops produces an effect upon the color of objects within the room. Any strong color on the wall will furnish a colored component of the total light.

Shades and reflectors are used either to modify the colors of the radiating object or the brilliancy of the source, so as to keep too bright a light out of the eyes, or to modify the distribution of light so as to put it where it will be of most service.