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Fluorescent
Lamp Parts
Basically, a fluorescent
lamp is made up of five
components. See Figure
5.1.
-
GLASS TUBE, coated on the
inside with fluorescent
powders called PHOSPHORS.
-
Two ELECTRODES (or cathodes)
coated with EMITTER, supported
by a glass mount structure,
and sealed at the ends of the
tube.
-
FILLING GAS - usually a low
pressure of Argon or
Krypton/Argon mixture.
-
Small amount of MERCURY
(less than 20 mg), which
vaporises during the lamp
operation.
-
LAMP CAP cemented to each
end of the tube to connect the
lamp to the lighting circuit.
Figure 5.1.
Fluorescent Lamp Operation
When the circuit is
energised, electricity heats the
cathodes. See Figure 5.2.
The cathodes are coated with
material which, when heated, emits
electrons. The electrons establish
an electric arc between the
cathodes at opposite ends of the
tube. The electrons collide with
the mercury atoms, causing mercury
to emit invisible ultra-violet
radiation. The ultra-violet is
absorbed by the phosphor coating
on the tube and re-radiated as
visible light.
Figure 5.2. Principles of
fluorescent lamp operation.
Fluorescent Lamp Shapes
Fluorescent lamps have a limited
range of shapes. Most common is
the straight tube in various
diameters. See figure 5.3.
The diameter may be
quoted in mm, but the universal
term is "T" for tube
followed by the diameter in
eighths of an inch e.g. 26mm is
T8. Most T12 lamps are now being
replaced by more energy efficient
T8 lamps of the same length but
reduced power.
Figure
5.3.
Fluorescent
tube
diameters.
U-shaped
fluorescent
tubes
offer an
alternative
configuration,
being
shorter
and with
the lamp
cap(s) at
one end.
See Figure
5.4.
Mod-U-Line
tubes can
fit into
600 mm x
600 mm
ceiling
luminaire,
compared
with 600
mm x 1200
mm
luminaire
for
straight
tubes. The
biaxial
shape has
a single
lamp cap
with
either two
or four
pins - GE
trademark
BIAX. More
information
on these
lamps is
given in
the
Compact
Fluorescent
Lamp
section.
Figure
5.4.
U-shape
fluorescent
lamps. |
