All supply undertakers are anxious to develop the consumption of electricity for power purposes even more than for lighting, but the first cost of installing electric motors is a deterrent to the adoption of electricity in small factories and shops, and most undertakers are therefore prepared to let out motors, &c., on hire or purchase on varying terms according to circumstances.
A board of trade unit will supply one 8 c.p. carbon lamp of 30 hours or 30 such lamps for one hour. In average use an incandescent lamp will last about 800 hours, which is equal to about 12 months normal use; a good lamp will frequently last more than double this time before it breaks down.
A large number of towns have adopted electricity for street lighting. Frank Bailey has furnished particulars of photometric tests which he has made on new and old street lamps in the city of London. From these tests the following comparative figures are deduced:—
| Average total Cost per c.p. per annum. | |
| Gas— | |
| Double burner ordinary low pressure incandescent (mean of six tests) | 11.1d. |
| Single burner high-pressure gas | 9.0 |
| Double burner high-pressure gas | 11.7 |
| Arc lamp— | |
| Old type of lantern | 8 |
| Flame arc | 5 |
From these tests of candle-power the illumination at a distance of 100 ft. from the source is estimated as follows:—
| Candle Ft. | Ratio. | ||
| Double ordinary incandescent gas lamp illumination | 0.013 | = | 1.0 |
| Single high pressure ordinary incandescent gas lamp illumination | 0.016 | = | 1.24 |
| Double high pressure ordinary incandescent gas lamp illumination | 0.027 | = | 2.10 |
| Ordinary arc lamp | 0.060 | = | 4.50 |
| Flame arc lamp | 0.120 | = | 9.00 |
The cost of electricity, light for light, is very much less than that of gas. The following comparative figures relating to street lighting at Croydon have been issued by the lighting committee of that corporation:—
| Type of Lamp. | Number of Lamps. | Distance apart (yds.) | Total Cost. | Average c.p. per Mile. | Cost per c.p. per annum. |
| Incandescent gas | 2,137 | 80 | £7,062 | 839 | 15.86d. |
| Incandescent electric | 90 | 66 | 288 | 1,373 | 13.71 |
| Electric arcs | 428 | 65 | 7,212 | 10,537 | 11.32 |
Apart from cheaper methods of generation there are two main sources of economy in electric lighting. One is the improved arrangement and use of electrical installations, and the other is the employment of lamps of higher efficiency. As regards the first, increased attention has been given to the position, candle-power and shading of electric lamps so as to give the most effective illumination in varying circumstances and to avoid excess of light. The ease with which electric lamps may be switched on and off from a distance has lent itself to arrangements whereby current may be saved by switching off lights not in use and by controlling the number of lamps required to be alight at one time on an electrolier. Appreciable economies are brought about by the scientific disposition of lights and the avoidance of waste in use. As regards the other source of economy, the Nernst, the tantalum, the osram, and the metallized carbon filament lamp, although costing more in the first instance than carbon lamps, have become popular owing to their economy in current consumption. Where adopted largely they have had a distinct effect in reducing the rate of increase of output from supply undertakings, but their use has been generally encouraged as tending towards the greater popularity of electric light and an ultimately wider demand. Mercury vapour lamps for indoor and outdoor lighting have also proved their high efficiency, and the use of flame arc lamps has greatly increased the cheapness of outdoor electric lighting.