THE HOSPITAL LIGHTING QUESTION

New Zealand Times, Volume XXXII, Issue 7319, 24 December 1910, Page 12

THE HOSPITAL LIGHTING QUESTION

mSB following ie i th© enclosure sent to the Hospital Board in the letter, from the Gas Company; EXTRACT FROM /'THE GAb* WORLD." NOVEMBER sth, 1910.P. 559. QUESTIONS AND ANSWERS. ; (1,476) FOEMHLA TOE CO.MPAEIson of costs of diffehent LIGHTS.—(I) Compare cost of. lighting with ordinary inverted incandescent gas, ( at 5s 5d per thousand, and electricity,, showing the .price at which the latter; must be supplied to give the same light.* Quote figures in support, showing method; of arriving at cost of lighting for all the| variety of electric lamps, especially me-i tailic filament lamps, for which an elcc-j trical engineer claims a consumption of; only 1.5 watts ner candle. (2) Show any disadvantage pertaining to various systems as regards maintenance. (3) State commercial value' of free water-power over, any, other power for generating electricity.—B.G.O.

(1) simple method of comparing the cost of lighting with any two: illuminknts, where tne consumptions of the different agents are known, and the price, is found- from the formula—Cequals w x p plus r. Where C is the cost in any. convenient unit—usually p<?nc© are taken : of 1000 hours* use of the particular lamp, w is the number of watts or the number of cubic feet of gas per hour, required by the ,lamp, P is the price per thousand cubic or per unit, and r is the cost of rehewing the lamp or the mantle, or any phrt of the apparatus, during the 1000 hours. The formula is obtained bytaking the number of watts; or the number of cubic feet required per hour, multiplying by.the cost per ulut, or per* thousand cubic feet, and dividing byi 1000, Us representing the 1000 watt-j hours of a Board of Trade electrical] unit and the 1000 cubic feet of gas upon which the charge for .gas is based., Tho figure 1000, appearing in both mi-, nlerator and denominator, cancels out., Applying the formula to the case quoted,', and allowing two mantles, at a cost of' gd each, and the rate mentioned 5s sdi oer thousand cubic feet, and allowing a consumption cf 8 cubic feet per hour t for a 60-candl© lamp, the formula works* out thus—C eqtials 3 x 65 plus 6 -equals 201 d. Talcing the formula t as ■ above, C eq. w x p phis H, it 'will be seen that it may be written C minus r cq. 1 C minus r w x p, and, therefore* p eq. This formula will enable us to find the price, at which electric current must be sold for ahy given electric lamp, taking ! current at a given rate, to equalthe cost by gas at the figure given in the question. Applying tho formula to the metallic filament incandescent lump, and allowing one lamp at 2S 6d foi* the ±OOO hours, 201 minus 30 the figures come out p eq. 5 : ■ ’ , 75 171 e q. eq. 2.28 d, or, say, 2-id per 75 Board of T¥adc> unit. In the above we have allowed the consumption of electricity by the metallic filament lamp at the rate at which it is now usually taken, viz., watts per candle. There are lamps on the market for which a consumption of only X watt per candle is claimed. We have also allowed 1000 hours as the life of a 60candle metallic filament lamp. "8.G.C." can discount these figures as much as his experience will nave, shown him. On tho other hand, gas lighting engineers claim that tho inverted mantlefurnishes a 60-candlo light for a consumption of 2 cubic feet per hour. If that figure is taken* it brings the price at which the electric current must be supplied, with the metallic filament lamp, down to under per unlc. With the arc lamp, the consumption of electricity Per cahdle-powsr is in the neighbourhood of O-o watt. In some calculations wo made a Short while since, we found the cost of arc lamps. Worked out on the formula given above* ranged from c£6 10s to £7 5s per 1000 hours* as against high-pressure gas lamps, <£3 5e td <£B 10s. - . (2) The metallic filament lamp and the incandescent gaS mantle are both subject to the disadvantage that the light given lessens with age, and in both cases the lessening of the light , depends iipoh the working conditions. With the incandescent electric lamp, variations of pressure, such as are very common in town set*: vice mains, have a very_ bad effect* The disadvantage of the arc lamp over the

high pressure incandescent gas lamp is the fact that the are lamp requires a certain amount of attention* With tho enclosed arc lamp, however, this has been reduced to a minimum.

(3) The commercial value of free Water power for generating electricity depends entirely upon the conditions under which the water-power is obtainable, the principal condition being the distance from the point of distribution. Water-power caves coal, but as against the saving of cddl, there is the interest upon the transmission line, and the cost of the Upkeep of the line. If the water-power is at a considerable distance from the town to be supplied, for instance, the interest and upkeep may more than equal the cost of the coal that is saved. A striking instance of this is the case of the Victoria Fails* on the' Zambesi. They are a very, great distance from the Hand, and the proposal that was made some little While back, to utili.se them for aupplying power to the Hand, in place of burning coal there, though the local coal is very poor, was practically laughed out of court- On- the other hand; again, the power of Niagara :© being utilised at Buffalo, some twentytwo miles away, for lighting and power."