40 



An irregular surface, bubbles, etc. in glass act as lenses and 

 affect the even diffusion of light. 



New glass is slightly superior to used glass. The deterioration 

 from dirt and other factors is much less than 1 percent, per annum. 



The more nearly the angle of the roof coincides T\-ith the right 

 angle of the sun's rays the more light is transmitted. 



Relatively steep roofs are superior to flat roofs for transmitting 

 light. Records made in February- show that a house with a 

 roof angle of 46° gave IS percent, more light than one with a 32"* 

 angle roof. 



The reflection of light from surfaces varies greatly. In our 

 experiments we found aluminium bronze to constitute the best 

 reflector of light. 



The practice of lapping glass causes som.e loss of light, an 

 average of 11 percent . in our tests. 



There appear to be no important differences in the light in a 



greenhouse at different distances from the glass, practically the 



same light being obtained at 5 feet as at 30 feet. The light to be 



had directly under the glass, however, varies in intensity owing 



-to the irregularity of the surface. 



The loss of light from glass may vary from 13 to 36 percent, or 

 more, depending on the quality and condition of the glass, and 

 many other factors. 



Double glazed houses are much inferior to those glazed with a 

 single layer of glass. 



