184 COMMISSION ON BUILDING DISTRICTS 



square foot and the corresponding working minimum 280 candles per square 

 foot. The illumination received at an unobstructed point on the surface of 

 the earth is 880 foot candles. The illumination on the side of a building 

 at the ground level where half of the sky is obstructed is 440 foot candles. 



Illumination on street 



Increasing the height of buildings reduces the amount of daylight fall- 

 ing on both the street level and the street facade. A street improved with 

 buildings once the street width in height receives only 71 per cent as much 

 illumination from the sky at the curb level as one improved with buildings 

 half the street width in height. For a street improved with buildings twice 

 the street width in height the direct illumination from the sky is only 42 per 

 cent ; thrice the street width, 29 per cent ; four times, 22 per cent ; five 

 times, 18 per cent ; and six times, 15 per cent. 



Illumination on street facade 



The illumination on the street facade diminishes even more rapidly 

 with an increased height of buildings than that at the street surface. A 

 point on the facade once the street width below the top of the opposite 

 buildings receives only 53 per cent as much direct daylight illumination as 

 one situated half that distance down from the top. At a point twice the 

 street width below the top of the opposite buildings across the street the 

 illumination is only 19.2 per cent of that one-half times the street width 

 down from the top ; three times the street width, 9.4 per cent ; four times, 

 5.5 per cent; five times, 3.5 per cent; and six times, 2.5 per cent. 



The illumination in foot candles in the street and on the street facade 

 due to direct skylight is shown in the following table for different points 

 below the top of the buildings assuming the street in each case to be uni- 

 formly improved on both sides with buildings of different heights. The 

 curve in Figure 60 presents this data in graphic form. 



Height of Buildings 

 Times Street Width 



Foot Candles 





On Street Level 



On 



Street Facade 







880. 







440. 



y 2 



486.8 



243.3 



l 



345.2 



128.9 



w 



1/2 



2 



296.4 



258.1 



204.0 



96.5 

 73.9 



46.6 



2/ 



3 



167.5 



141.6 



31.6 

 22.9 



4 ... 



107.7 



13.2 



5 



86.6 



8.6 



6 



72.5 



6.2 











Illumination in inner courts 



The minimum size prescribed by the Tenement House Law for an inner 

 court on the lot line in a tenement 60 feet high is 12 feet by 24 feet. The 

 law contemplates that this court should be complemented by a court of 

 similar size on the adjacent lot, but it does not enforce this provision. Let 

 us assume that the adjoining building when erected does not have its courts 



