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THE NATURE OF LIGHT
Such light is called a diffused light, thus, on a cloudy or hazy day, the light of the sun is diffused by its many reflections and re-reflections from the particles of watery vapor in the atmosphere. On a clear day the direct rays of the sun cast a dark shadow when any object is interposed between the sun and any surface upon which its rays fall, but when the light is diffused the reflected rays from many directions fall beneath the object, since the object is not in line with these reflected rays, and illuminate the surface beneath the object and we are not able to distinguish any perceptible shadows.
Practically all interior illumination is diffused light, for we can only have direct illumination where the sun shines through a window or other opening. We find it necessary to diffuse the light in interior scenes in order to make them appear natural, for it is not yet possible in the majority of cases to obtain sufficient illumination in an actual interior to act upon a photographic film with sufficient intensity in the short time of the exposure necessary with the motion picture camera. We have to build our interior sets in a studio using the artificial lighting equipment to produce the proper effect. This equipment may be Cooper-Hewitt mercury arcs or the usual carbon arc behind spun glass screens. If the stage is an open platform, exposed to the sky, using natural or daylight for illumination it becomes necessary to suspend screens of thin white cloth called diffusion or halation screens above the set, to break up and diffuse the direct rays of the sun.
We can all recall witnessing interior scenes taken in the direct sunlight where the pictures hung on the wall cast long oblique shadows and the characters, as they went through their actions on the screen, were each accompanied by a funereal silhouette which mocked every gesture in grotesque distortion upon the floor or wall. Happily, such scenes have now passed into the limbo of fading memories. When artificial lights are used, such as arc lamps, the light is diffused by ground or ribbed glass screens or with tracing cloth or similar material. The tubes of Cooper-Hewitt lights cover such an area that it is not usually necessary to use a screen for them, for the light, coming from so large an area covered by the tubes, is already sufficiently diffused.
WThen we produced the spectrum by passing a ray of light through a glass prism we found that the beam of light was bent
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