Page:Incandescent electric lighting- A practical description of the Edison system.djvu/144

 the case shown in Fig. 11, but the lamps are only half as good. The minimum total cost is increased from $294 to $327, and the maximum efficiency is reduced from 2.38 to 2.62 watts per candle.

Fig. 12.

The first and plainest inference drawn from these curves is that the maximum efficiency o£ any given lamp is not a fixed one, but varies with conditions outside