450 FERREE AND RAND— LIGHTING 



paratively evenly illuminated walls and working plane for the re- 

 flectors of medium density to the dark ceilings and upper part of 

 the room and highly illumined lower half for the opaque reflectors. 

 And with the opaque reflectors turned towards the ceiling, the trans- 

 lucent reflectors turned both up and down, and with reflectors of 

 both the focusing and distributing types, we have had the greatest 

 amount of light first in the upper half of the room, then in the 

 lower half, and within limits lanes of light have been produced ; 

 still it has been possible to get in all of these cases comparatively 

 good effects on the eye so long as no excessive brilliancies were in- 

 troduced in the field of view. Again, however, we do not wish 

 to say that this is the only factor that makes for the welfare of the 

 eye. We wish only to call attention to its very great importance. 



7. The problem of installing is not the same for the semi-in- 

 direct as for the totally indirect reflector. In the latter case the 

 height should be adjusted so as to give as nearly as possible an 

 even distribution of surface brightness on the ceiling and even- 

 ness of illumination on the working plane. In the case of the semi- 

 indirect reflectors, especially those of low and medium densities 

 and in rooms of medium height, if the distance from the ceiling is 

 made great enough to produce these effects, the bright reflectors 

 are dropped too low in the field of view for the highest comfort 

 and efficiency of the eye. Apparently the denser they are, the more 

 nearly they should be installed as are the indirect reflectors; and the 

 less dense they are the more nearly they should be installed as are 

 the direct reflectors of similar density, so far as eye effects of the 

 kind revealed by our tests are concerned. In this connection it 

 may be pointed out that in current practice direct reflectors for 

 general illumination are usually installed on the ceiling or as near 

 to it as is possible, especially in rooms of low and medium height. 

 However, while this may be a good general rule for the installation 

 of direct reflectors of low and medium density and of shallow and 

 medium depth, the question of most favorable height for the dense 

 and completely opaque reflectors is, we believe, still open to investi- 

 gation. 



8. In the work of providing general illumination the most diffi- 

 cult feature presented in the problem of protecting the eye is en- 



