CONTROLLED ENVIRONMENTAL CONDITIONS 



293 



Relative effectiveness of Mazda, neon, sodium vapor, and mercury vapor 

 lamps. Buckwheat seedlings ^' ^* were gro^\^l for 8 to 11 days under contin- 

 uous illumination from Mazda, neon, mercury vapor, and sodium vapor 

 lamps of equal intensity as determined by the Weston photronic cell, which 

 measures largely visible rays and has a light sensitivity similar to that of 

 the human eye. The temperature was about 77° F (25° C), the humidity 

 70 per cent, and the light intensity was 700 to 800 foot-candles, as agamst 

 a maximum of 900 in the constant-condition room. The lights were adjusted 

 as the plants grew, to keep the intensity at the tip of the plants constant. 

 Fig. 116A shows growth of buckwheat plants under neon lamps with 

 greenhouse-growTi check on left and Mazda light-grown check on right; 

 B shows the same for the sodium vapor lamp, and C for the mercury vapor 

 lamp. The artificial illumination was of course continuous 24 hours a day 

 in all cases, while the greenhouse check had less — 12 hours' daily illumina- 

 tion. One would judge from the relative heights of the plants in this pic- 

 ture that Mazda lamps gave much more growth than the other artificial 

 lights. When the gro^^i:h is measured by increased dry weight (Table 30) 

 the difference is less, or in case of the neon light the production is actually 

 greater than for the Mazda light. 



Table 30. Ratios of Dry Weight Produced under Each Lamp as Compared with the 

 Mazda = 1.00; Calculated from Table I'^; Weights in Grams per Plant 



The figures in the last column of Table 30 represent the dry weight which 

 might be obtained if equal energy value in the visible had been used. The 

 Weston photronic cell registers 98 per cent of the visible energy of the sodium 

 vapor light, 65.4 per cent of that of the neon, 62.4 per cent of that of the 

 Mazda, and 58.1 per cent of that of the mercury vapor. These figures are 

 taken into consideration in the calculation. For details on the calculation 

 the original article should be examined. ^^ Figuring on the efiiciency of the 

 energy in only the visible portion of the spectrum of sodium vapor and 

 Mazda lamps in increasing the dry weight of plants, the former is 1.41 to 1. 

 If the calculation for the relative efficiency of the two lamps were made on 

 the basis of the total radiant energy (including the infrared) the sodium 

 vapor would rank much higher, because the radiant energy of sodium vapor 

 is largely in the visible and that of Mazda lamp largely in the infrared. 

 In the constant-light room, as we have seen, A\'ith Mazda lamps supple- 

 mented by mercury vapor in glass, a fairly good growing light was obtained 



