138. The architect who designates the number and location of outlets for the lighting sources, and specifies the candle-power of the lamps, knows nothing of the ultimate decoration of the house. Very often the specifications are finished before the color scheme has been decided upon, and as a result the degree of illumination either falls short of what is needed in case of dark-colored interiors, or proves excessive with light-tinted rooms. The architect works from one point, economy,
139. We have to consider the mercury arc light, the yellow flame carbon, the white magnetite and titanium arc—all of high efficiency, giving orange yellow in the flame-carbon to yellow and yellow white in the acetyline of the tungsten filaments. Then we have the greenish yellow of the Welsbach mantle, the bluish green of the mercury arc, the yellowish white of the carbon arc, as well as the clear white of the titanium arc.
140. The subject may be divided into three heads: Quality, or approximation to natural light. Quantity, as demanded by reflection or absorption. Installation, diffusion or mechanical distribution.
141. Normal light is the light of general diffusion in daylight, and when we can find an artificial light that has the character of natural light we will have what is obviously the best illuminant for the home. Bear in mind that natural light as it appears out of doors is materially altered when indoors by the presence of different planes and angles, which cast and receive various depths of shadow; the quality required is that which will provide illumination without glare. The sun’s rays are softened and mellowed by the depth of air through which they pass, and it is this mellowness that is the chief requisite in illumination.
Good decorative illumination does not mean illumination that reveals every hidden corner of a room. We need shadows to betray form, relieve monotony and give depth to the ensemble. If in an illuminated area light is of a uniform intensity, we have a bad effect. The variation of tone in a fabric is due to the light reaching it from a given point. Differences in intensity make shadows and tones.
142. The illuminating engineer treats the home as he treats a public hall. He ignores the individuality of the room; the ball-room and the sickroom are lighted alike. He does not always consider the diminished force of light as it passes through a refracting surface, for it must be borne in mind that any method of indirect lighting by refraction is apt to cause a loss of volume. The use of various kinds of globes or lamp shades must all be considered. A light-colored wall reflects illumination, a dark-colored wall absorbs it; hence the amount of illumination is increased or diminished by the color of the walls.