3 oo 



WINDOWS AND SKYUGHTS 



fore, a general downward direction, varying with the time of day and 

 the position of the window. The portion of the room which receives 

 the most light ordinarily is the floor near the windows, but if we inter- 

 pose a dispersive glass in this beam the light will no longer fall t6 the 

 floor but will be spread out into a broad divergent beam falling with 

 nearly equal intensity on walls, ceiling and floor. There is of course 

 no gain in the total amount of light admitted, the light being simply 

 redistributed, taking up from the floor that which fell there and was 

 comparatively useless, and sending it where it is of more service. 



Experiments have shown that the diffusion of light in a room lighted 

 by means of windows or skylights depends upon the kind and position 

 of the glass used. The relative intensity of the light admitted in per 

 cents of the light outside the window for plane glass, factory ribbed 

 glass, Luxfer and canopy prisms is shown in Fig. 147*. 



Variation of Light 



with 

 Angle of Skylight 



No Direct Sunlight 



30 40 50 60 70 80 



Angle skylight makes with horizontal 

 FIG. 147. 



Fig. 147 shows a great increase in efficiency of factory ribbed glass 

 and prisms as the sky angle diminishes. 



*Report No. III. Insurance Engineering Experiment Station, Boston, Mass. 



