Artificial Lighting 181 



note that other colors are not rejected or reflected by the yellow 

 object. Try red paper in the green and yellow of the spectrum, and 

 note results. Does the red tend in the green light to become a green- 

 ish black as stated in connection with the color effect of the Cooper- 

 Hewitt light? What do you find to be the effect of the colors upon a 

 white object? How does black appear in each color? 



The facts seem to support the conclusion that the color of an 

 object depends upon the nature of the object itself and upon the 

 quality of the light which falls upon it. A yellow object is yellow 

 largely because it reflects or rejects yellow light. It absorbs 

 the lights of other colors. A pure white does not absorb any 

 of the colors of the spectrum, that is, it rejects or reflects all of 

 them to the eye. Black, on the contrary, rejects none of the 

 colors, but absorbs all, and remains black, therefore, in all quali- 

 ties of light. 



IV. GENERAL REQUIREMENTS IN ARTIFICIAL LIGHTING 



72. A good light. The types of lamps which we have con- 

 sidered are sufficient to indicate the main tendencies in artificial 

 illumination. Many other appliances for gas and electric 

 lighting are available, but they generally depend upon the 

 principles involved in the incandescent gas mantle, the carbon 

 or tungsten filament, in the arc, and in the mercury vapor or 

 vacuum lamp. They illustrate the same fundamental points 

 as to incandescence, resistance, radiation, and vacuum, in more 

 or less different forms. 



The commercial production of lighting appliances aims to 

 furnish an economical, efficient, and hygienic light. The initial 

 cost of the appliance, the cost of maintenance and operation 

 are always important in any form of lighting. The quality 

 and quantity of light produced are considered in connection 

 with the amount of gas or electric current consumed. The 

 quality of light and especially its hygienic characteristics are of 

 very great importance to the consumer. The essentials of a 

 thoroughly hygienic, safe, and useful light may be made topics 



