CH. XIII] 



RADIANT EFFICIENCY OF ARC LAMPS 



569 



water-cell. Of this 25%, 43% is light and the rest is infra-red. 

 This shows the advantage of using a water-cell as there is only 

 one quarter the heating effect with the water-cell as without it. 



With the alternating current arc, the corresponding figures are 

 approximately; Radiant efficiency (L/R) 6.4%, Water-cell effi- 

 ciency (W/R) 15.6%, and of the energy getting through the water- 

 cell (L/W) 41% is light. In this case it is seen that the water-cell 

 removes an even greater proportion of energy and hence its bene- 

 ficial effect is even greater with alternating current than with 

 direct current. For the practical application of these values, see 

 850, and fig. 342. 



778. Table showing the relation of light energy to the 

 total radiation of various light sources. 



(From the Physical Review, August, 1911) 



A. C. Alternating current. 

 Amps. Amperes. 

 C. P. Candle-Power. 



