here.

The efficiency (_i.e._, the light yielded per pint or other unit
volume consumed) of oil-lamps varies greatly, and, speaking broadly,
increases with the power of the lamp. But as large or high-power lamps
are not needed throughout a house, it is fairer to assume that the light
obtainable from oil in ordinary household use is the mean of that
afforded by large and that afforded by small lamps. A large oil-lamp as
commonly used in country houses will give a light of about 20 candle-
power, while a convenient small lamp will give a light of not more than
about 5 candle-power. The large lamp will burn about 55 hours for every
gallon of oil consumed, or give an illuminating duty of about 1100
candle-hours (_i.e._, the product of candle-power by burning-hours)
per gallon. The small lamp, on the other hand, will burn about 140 hours
for every gallon of oil consumed, or give an illuminating duty of about
700 candle-hours per gallon. Actually large lamps would in most country
houses be used only in the entrance hall, living-rooms, and kitchen,
while passages and minor rooms on the lower floors would be lighted by
small lamps. Hence, making due allowance for the lower rate of
consumption of the small lamps, it will be seen that, given equal numbers
of large and small lamps in use, the mean illuminating duty of a gallon
of oil as burnt in country houses will be 987, or, in round figures, 990
candle-hours. Usually candles are used in the bedrooms of country houses
where the lower floors are lighted by means of petroleum lamps; but when
acetylene is installed in such a house it will frequently be adopted in
the principal bed- and dressing-rooms as well as in the living-rooms, as,
unless candles are employed very lavishly, they are really totally
inadequate to meet the reasonable demands for light of, _e.g._, a
lady dressing for dinner. Where acetylene displaces candles as well as
lamps in a country house, it is necessary, in comparing the cost of the