must be in excess by about 15 per cent., in order to compensate for the
impossibility of obtaining equally well distributed illumination. These
assumptions are based on general considerations and data as to the effect
of sources of light of different intensities in giving practically the
same degree of illumination in a room; it would occupy too much space
here to discuss more fully the grounds on which they have been made. It
must suffice to say that they have been adopted with the object of being
perfectly fair to each means of illumination.

COST PER HOUR AND HYGIENIC EFFECT OF LIGHTING BY DIFFERENT MEANS

The data (except in the column headed "cost per 100 candle-hours") refer
to the illumination afforded by medium-sized (0.5 to 0.7 cubic foot per
hour) acetylene burners yielding together a light of about 100 candle-
power, and to the approximately equivalent illumination as afforded by
other means of illumination, when the lighting-units or sources of light
are rationally distributed.

Interest and depreciation charges on the outlay on piping or wiring a
house, on brackets, fittings, lamps, candelabra, and storage
accommodation (for carbide and oil) have been taken as equivalent for all
modes of lighting, and omitted in computing the total cost. The cost of
labour for attendance on acetylene plant, oil lamps, and candles is an
uncertain and variable item--approximately equal for all these modes of
lighting, but saved in coal-gas and electric lighting from public supply
mains.

______________________________________________________________________
| | | | | | |
| | |Candle- | Number |Aggregate| Cost |