The primary colors for this method of color-mixture are the same as those of the painter in mixing pigments—­namely, purple, yellow, and blue-green.  Various colors may be obtained by superposing or intimately mixing the colors.  The resulting transmission (reflection in the case of reflecting media such as pigments) are those colors commonly transmitted by all the components of a mixture.  Thus,

     Purple and yellow = red
     Yellow and blue-green = green
     Blue-green and purple = blue

The colors produced by adding lights are based not on the “subtractive” method but on the actual addition of colors.  These primaries are red, green, and blue and it will be noted that they are the complementaries of the “subtractive” primaries.  By the use of red, green, and blue lights in various proportions, all colors may be obtained in varying degrees of purity.  The chief mixtures of two of the “additive” primaries produce the “subtractive” primaries.  Thus,

     Red and blue = purple
     Red and green = yellow
     Green and blue = blue-green

Although the coloring media which are permanent under the action of light, heat, and moisture are relatively few, by a knowledge of their spectral characteristics and other principles of color the expert is able to produce many permanent colors for lighting effects.  The additive and subtractive methods are chiefly involved, but there is another method which is an “averaging” additive one.  For example, if a warm tint of yellow is desired and only a dense yellow glass is available, the yellow glass may be cut into small pieces and arranged upon a colorless glass in checker-board fashion.  Thus a great deal of uncolored light which is transmitted by the filter is slightly tinted by the yellow light passing through the pieces of yellow glass.  If this light is properly mixed by a diffusing glass the effect is satisfactory.  These are the principal means of obtaining colored light by means of filters and by mixing colored lights.  By using these in conjunction with the array of light-sources available it is possible to meet most of the growing demands.  Of course, the ideal solution is to make the colored light directly at the light-source, and doubtless future developments which now appear remote or even impossible will supply such colored illuminants.  In the meantime, much is being accomplished with the means available.

XXII

SPECTACULAR LIGHTING

Artificial light is a natural agency for producing spectacular effects.  It is readily controlled and altered in color and the brightness which it lends to displays outdoors at night renders them extremely conspicuous against the darkness of the sky.  It surpasses other decorative media by the extreme range of values which may be obtained.  The decorator and painter are limited by a range of values from black