International projectionist (Jan-Dec 1950)

• LOOKING BACK-TO THE FUTURE • This department, a regular IP feature, is a review of fundamental technical data. The Language of Lighting II. COLOR COLOR is a pleasing visual experience which nature has used extensively to give variety and beauty to the landscape and the sky overhead. The brilliance of the flowers, the green of the trees, the radiance of the sunset, and the multicolors in the rainbow, all present a kaleidoscope to stimulate interest in color and to excite human ingenuity to duplicate it artificially, that this visual experience may be brought under man's control and applied whereever desired, day or night, independent of nature. To achieve' this, in so far as it is possible to do so with light, one must, of course, know something of the theory of color. It is necessary, first of all, to become familiar with some of the fundamentals of color terminology. A color is characterized by three qualities — hue, brilliance and saturation. Color Terminology Hue. It has already been shown that hue, the fundamental quality of all colors, is determined by the frequency of the ether vibrations; thus hue is determined by the position in the spectrum and is identified as red, blue, etc. Brilliance. A color of a certain hue may be dark or light. This has nothing to do with the frequency of the ether vibrations, but depends on the amount FIG. 6. Color mixture by addition of wavelengths of light. of light reaching the retina of the eye in a given time. This characteristic of a color which causes it to appear as dark or light is known as its brilliance, luminosity or brightness. Saturation. If to a color of one wavelength— red, for example — white light consisting of all visible wave-lengths is gradually added, the red becomes paler and paler. In its original condition, this red is regarded as a pure color and is said to be perfectly saturated. It becomes less and less saturated as the white light is added. Almost all colors seen in ordinary life are due to selective reflection of white light, and since some portion of all the wave-lengths is reflected, these colors are usually far from saturated. When a leaf is seen by sunlight, for example, it appears green because the leaf reflects the green wave-lengths more efficiently than any of the others. However, it does not completely absorb all other wave-lengths ; nor does it reflect all the green. It should be emphasized at this time that a color is by no means a simple elementary phenomenon but a complex psychological state, depending not only on whether the stimulating ether vibrations are long or short, or the level of the light high or low, but on many other factors as well. Among these might be mentioned the condition of the retina with respect to its previous stimulation (state of adaptation) ; the stimulation taking place in neighboring portions of the retina (contrast) ; the part of the retina being affected by the light, and the duration of the stimulus. These factors combine to give rise to an almost endless variety of colors, equalled only by the variety of names which fashion experts, and others, find to attach to them. It is instructive to observe that in spite of all these complications, visual sensations are of such a nature that all colors, including white, can be produced by combining three properly selected primary colors according to certain laws of color mixing. Color Mixing Methods There are two methods of color mixing, the additive and subtractive. If on a screen a blue beam and a separate yellow beam of light are projected, the portion where they overlap will be white. These colors are, therefore, said to be complementary, and this method of com bining colored beams is called the additive method of color mixing. The tendency in this method is always to produce more light and to approach white. The primary colors for the additive method are red, green, and blue. Red and green combine to give yellow and all the intermediate shades; red and blue give magenta, and green and blue give a blue-green. This method of colormixing is illustrated in Fig. 1. If a beam of white light is made to pass through a piece of yellow glass and a piece of blue-green glass placed behind one another, the light passing through will be seen as green. This is called subtractive color mixing, and the tendency in such cases is to obtain less light and to approach black. The three primaries for subtractive mixture are the exact complements of those for the additive method. These are blue-green, magenta, and yellow (Fig. 2). They are approximately the blue, red, and yellow which are used in painting. Colored pigments, when mixed, behave according to the laws of subtractive mixture. In the application of light, wide use is found for both the additive and subtractive methods. Producing Colored Light Gaseous tubes are coming into wide use for the production of colored light. Filters which absorb all the colors except the one desired from an incandescent source are also widely used for this pur FIG. 7. Color mixture by subtraction of wavelengths of light. pose. For example, if red light is to be produced, white light is passed through a red-colored filter. Various substances are used for filters such as glass, gelatin, (Continued on page 28) INTERNATIONAL PROJECTIONIST February 1950 19