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Electrical Applications 2 by David W. Tyler

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7 Illumination
Aims:
At the end of this chapter you should be able to:
State that light is emitted by hot tungsten wire in an
incandescent
lamp and an
electrical discharge
in a gas.
Compare efficiencies and colour
spectra
of
various
lamps.
Define flux, intensity,
illuminance
and luminance.
State the
inverse
square law.
Calculate
the illuminance of
a
surface using E = I cos θ/d
2
and a
polar diagram.
Calculate the number of luminaires needed to provide uniform
lighting using the lumen method together with maintenance and
utilisation factors.
Describe
the effects of diffusing and prismatic
luminaires.
State the conditions
which
affect the amount of
daylight reaching
a
point in a room.
White light may be resolved into a band of colours called the spec-
trum ranging through red, yellow, green, blue and violet by passing