The number of gas lights which are actually used at one time in a house is found to average only two-thirds of the total number fixed, and with electric light this number is reduced to one-half; economy is at once the rule with electric light, partly because of the novelty of the illuminant, and also on account of the facility of lighting and extinguishing by simply turning a tap or switch. The number of hours artificial light is wanted in a residential district may be taken at about 1000 hours per annum, that is to say, the light is required for about four hours a day in winter and two hours in summer; this amount is very much exceeded in clubs, shops, and even in large houses, but 1000 hours is a safe figure, and, if the supply is taken by meter, an annual payment equivalent to 1000 hours’ supply should be a fixed amount to be paid for, whether used or not. Mr. Crompton estimates that a Londoner, who is a tenant or owner of a house having three reception rooms, ten bedrooms, and usual offices, spends about £25 a year for his lighting, which is made up as follows:—gas bill, £15; lamp, oil, candles, matches, about £10. There would be about fifty burners fixed; and, supposing fifty electric lights to be substituted, he could be supplied with electricity for £25 a year, at a fair profit to the supply company if they charged 8_d._ per Board of Trade Unit, as practice has shown that the total number of lamp-hours with fifty electric lamps is not more than sixty-two, so that two Units,[1] or 1_s._ 4_d._ per day, would be sufficient for the lights he would require. [1] Unit; see page 7.