560 CANDLE-POWER OF ARC LAMPS [Cn. XIII 



drawn from the line to the extent of 15x110 = 1650 watts. 

 Hence, in fig. 304 there are drawn two curves for direct current, one 

 for the power consumed at the arc, and the other for the power drawn 

 from the line with a no volt supply when used with resistance. 



With alternating current there are even more possibilities. 

 There is the power consumed at the arc, the power drawn from the 

 no volt line with resistance, and the power drawn from the line if a 

 suitable transformer of high efficiency is used. In calculating the 

 power consumption when using a transformer the actual power 

 consumed at the arc was divided by the efficiency of the trans- 

 former. Thus with 10 amperes alternating current the right-angle 

 arc consumed 430 watts at the arc. The transformer had 96% 

 efficiency, hence the power drawn from the line was 430 -=- .96 = 

 450 watts. In addition, curves were drawn showing the power 

 consumption when a rectifier was used. 



767. Results. The results as shown in figures 302-304 are, 

 that with the same amount of power drawn from the line, the least 

 light is given when alternating current is used with a rheostat and 

 the most when alternating current is used with a rectifier. With 

 the right-angle arrangement there is more light for the same power 

 with direct current and a rheostat, than with alternating current 

 and a transformer, but with inclined carbons there is but very little 

 difference in the light given for the same power supplied, whether 

 alternating current is used with a transformer or direct current is 

 used with a rheostat. It is to be noticed, however, that by using 

 sufficient power it is possible to get more light by the use of direct 

 than with alternating current. 



The power drawn from the line depends on the power consumed 

 at the arc and the efficiency of the ballast or transforming device. 



768. Efficiencies with different arrangement of carbons, and 

 different forms of current. The efficiencies of these devices are : 



With ripht-angle Inclined 

 ca.bons carbons 



Direct Current and rheostat = 50% = 46% 



Alternating Current and rheostat = 45% = 2 7% 



Alternating Current and transformer = 96% = 96% 



Alternating Current and rectifier = 70% = 70% 



