Page:Incandescent electric lighting- A practical description of the Edison system.djvu/133

 efficiency the cost of operating the lamps is a minimum, and this I call the maximiun efficiency of those lamps.

The following examples show what this maximum efficiency is, under varying conditions of the cost of lamps, the cost of current and the quality of the lamps. The coat of the lamps I have varied between 25 cents and $1.00 each. The cost of current varies between 2.5 cents and 10 cents per h.p, per hour. The quality of the lamps varies between 300 hours life at 3 watts per candle, and 2,400 hours life at 3 watts per candle.

In each of the following cases I have calculated the cost of operating 100 16 c, p, lamps 1,000 hours, at each of the efficiencies comprised in the curve of total cost. These curves do not show the cost of running the same lamps at different efficiencies, but the cost of running equally good 1 G candle lamps of the different efficiencies.

The first case we will consider is shown in the diagram Fig. 3. In this case the lamps are assumed to cost 85 cents each