448 ALTERNATING CURRENT* 



them. In street lighting, on the other hand, the objects illumi- 

 nated are the street and sidewalk surfaces, trees, etc., all of which 

 are dark in tone, and any light not falling directly on thorn is 

 lost. The light reflected from buildings is so small that it need 

 not be seriously considered. The light which goes upwards 

 and into trees is lost. 



Formerly, the idea of good street lighting was to imitate day- 

 light as closely as possible by securing uniform illumination. 

 Those responsible for the design and placing of street lighting 

 units directed their efforts towards obtaining this result and 

 the greater the uniformity the more successful the installation 



FIG. 404. Road objects recognized by silhouette. 



was considered. This method of illumination has one fault 

 which was not appreciated at first. With the dim illumination 

 which necessarily accompanies street lighting, objects are seen 

 mostly by shadow and silhouette. This is illustrated by Fig. 404, 

 in which the automobile is recognized almost entirely by its 

 silhouette. With uniform lighting, obtained by using a large 

 number of small units placed close together, shadows and silhou- 

 ette are almost entirely eliminated. Depressions and objects 

 in the road become much more difficult to distinguish. This is 

 particularly true when the object and the road have the same 

 general color. 



