CONTROLLED ENVIRONMENTAL CONDITIONS 



287 



Table 29. With Electricity at 2c per Kilowatt Hour, What Was Sunlight Worth per 

 Acre for Each Average Day During the Year 1936? 



{The figures are calculated from New York Meteorological data) 



ing by giving a rapid exchange of air about the lamps. WTiile Mazda lights 

 have about 90 per cent of their energy in the infrared, this cooling reduced 

 the heat ray to about 50 per cent, about the proportion of heat to light ray 

 existing in sunlight. The light reaching the plants, however, was dominantly 

 red-yellow, so mercury-vapor lights in glass tubes were burned along the 

 walls of the growing chamber to increase the blue-\aolet rays. Even ^^'ith this 

 enrichment, the light in this room was dominantly red-yellow as compared 

 with daylight. With all 25 1500-watt lights burning, the intensity of the 

 light in the gro^^^ng room was about 900 foot-candles. This is a low inten- 

 sity compared with the maximum of sunlight at Yonkers at noon in June, 

 which is about 10,000 foot candles. The light in the room, however, was 

 constant for 24 hours of the day, whereas that in nature is markedly variable 

 during the day, and is non-existent at night. ^\Tien 25 1000-watt lamps 

 were used or when only a portion of the 25 lamps were on, the intensity of 

 the light was lower. The same was true after the lamps began to age. To 

 avoid the reduction in intensity due to aging of the lights, they were 

 changed after 40 to 45 days of constant burning, or the experiments were 

 limited to this period. During some of the experiments the intensity of the 

 light in this room was as low as 350 foot-candles. 



In most of the experiments the temperature of the room was held at 

 78° F (26° C), but runs were also made at 68° F (20° C). This proved for- 

 tunate in the study of the potato, as we shall see later. The CO2 in these 

 rooms was run at ten times normal, or 0.3 per cent * and the relative 



* The CO2 enrichment of the air in the constant-condition rooms was always accom- 

 phshed by use of tanks of Uquid CO2. Mostly the same was true of the greenhouses. For 

 two years the source of CO2 for one of the greenhouses was scrubbed flue gas from the 

 Institute boilers. To free the flue gases of all toxic or tarry materials, and at the same 



