562 CANDLE-POWER OF ARC LAMPS [Cn. XIII 



Direct current with a rheostat gives less light than alternating current with a 



rectifier. 



Direct current, if only the power consumed at the arc is counted, gives the 

 greatest illumination of all for a given power input, (left upper curve), 

 i.e., 10,000 candle-power for less than two kilowatts of power. 

 B Lamp with inclined carbons. 



Alternating current with a rheostat, the least light. 

 Direct current with rheostat, next. 

 Alternating current with a transformer, next. 



Alternating current with a rectifier gives the greatest illumination for the 

 power consumed. 



The upper left hand curve shows that direct current gives the greatest 

 amount of light if only the power consumed by the arc is considered and that 

 wasted in the rheostat is not counted. 



If the sets of curves for the right-angle lamp and those for the 

 inclined-carbon lamp are compared it will be found that the right- 

 angle lamp gives the most light for the same current in every case. 

 The light given for the same power input is the same with rectified 

 current for both styles of lamp. With either alternating or direct 

 current and resistance, the right-angle lamp gives the greater light, 

 but with alternating current and a transformer the right-angle lamp 

 gives less light. This is due to the higher voltage of the right-angle 

 arc when used with alternating current, the right-angle arc requir- 

 ing about 50 volts while the inclined carbon arc requires but 30 

 volts. 



In the table ( 763) is shown the power in kilowatts drawn from 

 the line for different intensities of the light. This table was made 

 from the curves in fig. 3046 and applies to the inclined carbon 

 lamp, with no volt supply. 



In the table ( 764) is shown the candle-power for different 

 amounts of power consumption. 



769. Distribution of intensity in the different directions with 

 the different forms of projection arc. Fig. 305-306 show the dis- 

 tribution of light around the different forms of arc lamp. The 

 distance from the center to the curved line gives the candle-power 

 of the lamp in the given direction. Fig. 305 shows that the right- 

 angle arc has 3,750 c. p. in a horizontal direction, 4,000 c. p. 15 

 below the horizontal, and 2,900 c. p. 15 above the horizontal. 

 These curves show the results of actual experiments. The light 

 coming mostly from the crater, a slight change in the position of the 



