Artificial Lighting 177 



industries has opened a field for a very different and interesting 

 type of electric lamp. In all industrial work where artificial 

 light is necessary, certain definite requirements are made as 

 to the quality, intensity, and distribution of the light. A 

 light in any workroom must be intense enough without glare 

 to enable the worker to see easily and clearly and not to 

 blind or fatigue the eyes. It must be steady, unflickering, 

 and must not cast sharp and deep shadows. The matter of 

 safety and cost is of great importance. 



The usual standard of light is sunlight or daylight. There 

 is not at present any artificial light which equals sunlight in 

 quality, intensity, and distribution. Sunlight is " white 

 light," a light, that is, in which no color predominates. In 

 artificial lights of the incandescent or arc types all the colors 

 are combined but in a different proportion from that of day- 

 light. The result is that the artificial lights do not give a 

 perfect " white light." 



It is known that certain colors are more fatiguing to the eye than 

 others. Those who have experience in developing photographic 

 negatives, know that red light has no effect upon the film or 

 plate ; while the colors at the other end of the spectrum (page 

 180) have a chemical effect or are photographically active. 

 One cannot see, however, as well by red light as by yellow or 

 green. Experiments prove that a pure green light is about 

 eighty- three times as efficient for seeing purposes as a red light. 

 It is also known that a one-color light is better in illumination 

 than a many-color light. It has what is called the quality of 

 visual acuity or sharpness. It brings details out clearly. These 

 conditions are largely met by what are known as vapor lamps. 

 Such lamps give light only by means of luminous vapor or gases 

 and they are restricted to certain colors of the spectrum. The 

 best known are the Cooper-Hewitt mercury vapor lamp and 

 the Moore vapor lamp. The latter makes use of carbon dioxid 

 as the gas and gives a white light. The Cooper- Hewitt lamp 

 is widely used in industries of almost every kind, such as metal 



