Conversely, the more powerful and intense any single unit of light
is, the more is it liable to injure the eyesight, the deeper and, by
contrast, the more impenetrable are the shadows it yields, and the less
pleasant and artistic is its effect in an occupied room. For economical
reasons, therefore, one large central source of light is best in an
apartment, but for physiological and aesthetic reasons a considerable
number of correspondingly smaller units are preferable. Even in the
street the economical advantage of the single unit is outweighed by the
inconvenience of its shadows, and by the superiority of a number of
evenly distributed small sources to one central large source of light
whenever the natural transmission of light rays through the atmosphere is
interfered with by mist or fog. The illuminating power of acetylene is
commonly stated to be "240 candles" (though on the same basis Wolff has
found it to be about 280 candles). This statement means that when
acetylene is consumed in the most advantageous self-luminous burner at
the most advantageous rate, that rate (expressed in cubic feet per hour)
is to 5 in the same ratio as the intensity of the light evolved
(expressed in standard candles) is to the said "illuminating power.
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