182 COMMISSION ON BUILDING DISTRICTS 



The quantity of sunshine admitted in terms of cubic foot sun hours 

 by our standard window, the center of which is located at different distances 

 below the top of the opposite buildings is indicated in the following table. 

 This table shows the quantity of direct sunshine admitted by a window set 

 in a wall 14 inches thick, one eight inches thick and one of infinitesimal 

 thinness. 



Window Opening on North and South Street 







Cubic Foot Sun Hours Admitted bv Standard Window 



Distance of 

 of Window 



Center 

 Below 









In Wall 



In Wall 



1 



Top of Opposite 



Fourteen 



Eight 



In Wall 



Buildings ir 



[ Terms 



Inches 



Inches 



of Infinitesimal 



of Street Width 



Thick 



Thick 



Thinness 



.0 





267.1 



312.9 



391.2 



.1 





189.2 



232.8 



316.9 



.2 





138.4 



168.1 



248.0 



.3 





84.1 



132.0 



184.2 



.4 





54.4 



88.7 



158.4 



.5 





35.2 



62.4 



135.2 



.6 





24.0 



47.9 



108.8 



.7 





14.6 



33.6 



84.8 



.8 





9.2 



24. S 



63.9 



.9 





5.3 



19.2 



55.2 



1.0 





2.8 



18.2 



46.2 



Statement p.v Herbert S. Swan and George W. Tuttle, of the Staff 

 of the Committee on the City Plan, March 31, 1916 



In the lighting of buildings, daylight is more important than sunshine. 

 Daylight is the sunlight diffused and reflected by the sky and clouds as dis- 

 tinct from that received directly from the sun. Sunshine is obtained from 

 but one point, viz., the sun. Daylight, on the other hand, is obtained from 

 the whole visible sphere of the skv. 



Professor O. H. Basquin, of the American Luxfer Prism Company, in 

 1907 made a series of observations with a flicker photometer recording the 

 intensity of the zenith skylight at Chicago under varying conditions. These 

 measurements which were taken daily at 9 a. m., 12:30 and 4:30 p. m., 

 covering a two year period, showed the mean annual brightness of the zenith 

 sky at Chicago to be 500 foot candles per square foot. The intensity taken 

 as a working minimum was one-half of the mean annual brightness or 250 

 candles per square foot. This amount was generally available as a daily 

 average except on one or two days a month — on days with either a clear 

 blue sky or a stormy sky, both of these conditions giving a minimum illu- 

 mination. The sky at various altitudes gave substantially the same illumi- 

 nation as at the zenith. 



The curve showing the brightness of the sky follows quite closely the 

 mean daily and yearly sunshine curve. The per cent of annual sunshine 

 to the maximum possible varies in different cities of the United States all 

 the way from 36 to 84 per cent. In New York it is 58 per cent. The hourly 

 per cent of the maximum possible sunshine in New York is shown by the 

 curve in Figure 59. 



Assuming that Prof. Basquin's data for Chicago is true for New York 

 after allowing for the difference in the per cent of annual sunshine the 

 mean annual brightness of the zenith skv in New York is 560 candles per 



