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Electrical Applications 2 by David W. Tyler

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110 Illumination
Instead of using clear glass, the interior surface may be treated to
create the pearl lamp. This makes the filament appear to have a
larger area. If the light radiating capability is unchanged the lumi-
nance must have decreased. Where the lamp can be viewed directly,
the pearl lamp would be preferred. Alternatively where the lamp is
enclosed in some form of shade or diffuser, making direct viewing
impossible, the clear lamp would be quite suitable.
THE LUMEN AND THE
STERADIAN
Sphere
Figure 7.4
Figure
7.4
shows a light source with uniform luminous intensity of
1 candela at the centre of a sphere o