) Hence, in the tabular statement which
follows of the comparative cost, &c., of different illuminants, it will
be assumed that 30 good candles would in practice be equally efficient in
regard to the illumination of a room as large oil-lamps, acetylene
flames, or incandescent gas-burners aggregating 100 candle-power.
For the same reason it will be assumed that electric glow-lamps of low
intensity (nominally of 8 candle-power or less), aggregating 70-80
candle-power, will practically serve, if suitably distributed, equally as
well as 100 candle-power obtained from more powerful sources of light.
Electric glow-lamps of a nominal intensity of 16 candles or thereabouts,
and good flat-flame gas-burners, aggregating 90-95 candle-power, will
similarly be taken as equivalent, if suitably distributed, to 100 candle-
power from more powerful sources of light. Of the latter it will be
assumed that each source has an intensity between 20 and 30 candle-power,
such as is afforded by a large oil-lamp, a No. 1 Welsbach-Kern upturned,
or a "Bijou" inverted incandescent gas-burner, or a 0.70-cubic-foot-per-
hour acetylene burner. Either of these sources of light, when used in
sufficient numbers, so that with proper distribution they light a room
adequately, will be taken in the tabular statement which follows as
affording, per candle-power evolved, the standard illuminating effect
required in that room.
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