PHOTOMETRY AND ELECTRIC LIGHTING. 323 



It is very important in arranging for the illumination of a room 

 to place the lamps outside of the field of vision, if possible, so that 

 no light can enter the eye directly from the lamps and render the 

 eye insensible to the delicate shading of surrounding objects. The 

 excessive discomfort that is produced by the glare of improperly 

 located lamps, such for example as the exposed foot-lights of a 

 poorly arranged stage, is due not only to the physical pain that 

 is associated with long continued looking at a bright light, but 

 more especially to the incessant strain of trying to peer into the 

 dark region beyond. 



Where a lamp cannot be removed from the field of vision the 

 bad effects of glare may be greatly reduced by enlarging the 

 effective luminous surface of the lamp by means of a translucent 

 globe. A translucent globe always absorbs a considerable por- 

 tion of the light of a lamp, but the effectiveness of the globe in 

 eliminating glare is due primarily to the fact that a given amount 

 of light coming from a small brilliant source produces a much 

 greater glare than the same amount of light coming from a large 

 faint source. 



Dim lamps versus brilliant lamps. A much more satisfactory 

 distribution of light in a space to be illuminated may be obtained 

 by using several lamps of moderate brightness than by using one 

 or two lamps of great brightness. Thus very bright lamps are 

 not suitable for illuminating small rooms because the one or two 

 lamps required to produce the desired quantity of light give a 

 very unsatisfactory distribution, and the number of lamps required 

 to give a satisfactory distribution would produce an excessive 

 amount of light. To give a satisfactory distribution of light over 

 the field of vision in the lower portion of a room, very bright 

 lamps should be raised to a considerable height over head. In 

 general, therefore, very bright lamps are unsatisfactory, except for 

 lighting very large high rooms and for street lighting ; such 

 lamps may, however, be used satisfactorily in moderately small 

 rooms when the indirect system of illumination is employed. In 

 this system all of the direct light from the lamp or lamps is thrown 



