Cold Light

Collier's New Encyclopedia (1921)

or light without heat, is light from which the usually attendant infra-red rays or so-called radiant "heat" waves have been detached and eliminated. Ordinary sunlight is composed of waves varying varying in length from 15 mil lionths of an inch (violet light) to 28 millionths of an inch (red light); but the total radiation we receive from the sun, as well as from other sources of light, includes not only light waves, but other waves of greater length, invisible to the eye, but perceptible to the skin and called heat waves. Even the shortest waves may raise the temperature of bodies upon which they fall in some slight measure, but practically the short waves of light by themselves are "cold." To eliminate the longer waves from the radiant energy of any source of light is therefore the problem of producing "cold light." It has long been known that the light of the glowworm is practically unattended by the emission of heat, light production in this case being 96.5 per cent efficient, whereas the most efficient incandescent lamp emits as light only 2 or 3 per cent of the electrical energy consumed in its production, the remainder being given out as heat. In 1922, Prof. E. N. Harvey of Princeton University succeeded in isolating the substance by which the glowworm's light is produced. It is known as luciferin and is secreted by various other insects and marine animals which have the property of luminosity. When oxidized artificially, it produces cold light, but the practical value of the luciferin lamp must await the discovery of some method of producing the luciferin other than that COLORADO RIVER COMPACT of obtaining it in minute amounts from insects. Another kind of cold light has recently been obtained by means of an invention of Max J. Ritterrath of Los Angeles. The infra-red heat waves accompanying beams of light are separated from the light waves by means of refraction and the heat is absorbed and carried off by running water, or other fluids. Tests made on motion-picture films and explosives such as TNT prove that this filtered light is practically heatless. The possible applications of cold light in the sciences as well as in industry are numerous and important. COLDS. The causes and symptoms of common colds are now almost universally believed to be traceable to germs which are probably present in the air passages of the throat and lungs at all times and which are able to gain access to exposed membranes when for any reason the ordinary body resistance to infection is lowered, as, for instance, by sudden chilling of the skin, with the consequent diversion of the blood supply from the surface blood vessels and resulting congestion in other parts. Infection may arise without any chilling where the germs are numerous, as during epidemics of colds, or when the body resistance is not high; and, on the other hand, chilling is not necessarily followed by a cold where the body resistance is well-developed. Habit develops the mechanisms of resistance, so that a person accustomed to conditions of cold or wet may expose himself to these with impunity, whereas another person in the same circumstances will readily "catch cold." Bodily uncleanliness is conducive to colds, since the skin is then damp and so liable to sudden chilling, while the body resistance is apt to be reduced. Ordinary cold in the head is called coryza. (q. v.)