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42
The streets mentioned are at present lighted by 261 gas lamps
(including refuge lamps), giving a total candle power of about 5,800
candles, and costing £990 per annum, including cleaning, lighting and
extinguishing, but excluding repairs. The cost of lighting this route
by arc lamps depends, of course, upon the number and description of
lamps erected. Suppose, for instance, 63 300-watt arc lamps are
erected at a distance of 80 yards apart in the streets before-mentioned.
Taking 10 hours a day as a fair average throughout the year during
which the lamps will be alight, and assuming that cables are laid to
permit of half the lamps being turned out at midnight, the following
may be taken as the approximate cost of working, the cost of the
current being reckoned at 3½d. per unit (including sinking fund):—
63 arc lamps burning 5 hours per day =315 hours'
consumption of electricity per day; 315 X 365
= 114,975 hours'consumption of electricity per
year:—
114,975 x l.05d. (cost of current for a £ s. d.
300-watt lamp at 3½d. per unit) 503 0 3
32 arc lamps burning 5 hours per day= 160 hours
per day x 365 = 58,400:—
58,400 x l.05d 255 10 0
Total cost of working £758 10 3
To this amount should be added the cost of renewing the carbons
and fixing the same. The actual candle power of arc lamps depends
upon the angle at which it is measured. Professor Robinson gives
the average candle power of a 300-watt lamp at an angle of 20 degrees
at 322. Taking this average, the 63 arc lamps would give a total
candle power of 20,286, against that of 5,800 given by the gas lamps,
while there would be little or no appreciable difference in the cost.
If 500-watt arc lamps were used the cost would be more, and generally
speaking it would, perhaps, be safe to assume that street lighting by arc
lamps costs more than by gas, but that if calculations are made on the
basis of "light for light," the reverse would be the case. Your
Committee has come to the conclusion that the lighting of the route