Page:Incandescent electric lighting- A practical description of the Edison system.djvu/139

 the maximum efficiency of the lamps is 4.33 watts per candle.

In the case shown in Fig. 7 the lamps cost 50 cents and have a life of 1,200

Fig. 7.

hours at 3 watts per candle. The current costs 10 cents per h. p. per hour. This is the cheapest and also the best lamp we have yet considered, but the current is expensive. In this case the