Natural Light in Buildings
From the foregoing statement it is quite obvious that a proper amount of light, and if possible the direct rays of the sun, must be admitted to the home if it is to afford an environment at all conducive to the expression of life. It is therefore necessary to make special provision for the admission of light. The amount of light admitted to a building will be determined by its location and aspect, the source of the light, whether direct or reflected, the location and size of the openings, and the kind of glass used. The character of the walls and other inside surfaces will determine the light diffusion.
Since direct rays of the sun give more light than those reflected, it is desirable to admit them to the house as much as possible rather than to depend upon reflected light from the surfaces outside, such as the trees and buildings.
There is a certain loss of light as it passes through window glass. This loss is about 8% through plate glass while through double glass the loss is 10%, and through milk glass there is a loss of 50%. The amount of light in a room may be increased by the use of prism or ribbed glass which results in a more even distribution of light over the room.
The window area of rooms in a home should be not less than 10% of the floor area, or not less than one square foot of glass surface for every seventy cubic feet of interior to be lighted. This is not sufficient, however, for a schoolroom or for factories. The schoolroom should have a window area not less than one-fourth of the floor space.
Windows should be placed so as to admit direct rays of the sun and should extend within six inches of the ceiling. Window shades may be used to regulate the amount of light admitted, but care should be exercised in keeping down the dust, since it accumulates on the shades and is disturbed when they are adjusted. The dust then gets into the breathing zone and becomes objectionable from a hygienic standpoint.