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On/Off
switch
+
120 V
– 60 Hz
I filament
Black
White
White
Oil-impregnated
heat absorbing
material throughout
inside of container
Ballast
FIG. 21.49
(a) Schematic of single-bulb fluorescent lamp; (b) starter; (c) internal view of
ballast transformer.
fact, in an incandescent bulb, about 75% of the applied energy is lost in
heat, with only 25% going to light emission. In a fluorescent bulb more
than 70% goes to light emission and 30% to heat losses. As a rule of
thumb, one can assume that the lighting from a 40-W fluorescent lamp
[such as the unit of Fig. 21.48(a) with its two 20-W bulbs] is equivalent
to that of a 100-W incandescent bulb.
One other interesting difference between incandescent and fluorescent
bulbs is the method of determining whether they are good or bad.
For the incandescent light it is immediately obvious when it fails to give
light at all. For the fluorescent bulb, however, assuming that the ballast
is in good working order, the bulb will begin to dim as its life wears on.
The electrodes will get coated and be less efficient, and the coating on
the inner surface will begin to deteriorate.
Rapid-start fluorescent lamps are different in operation only in that
the voltage generated by the transformer is sufficiently large to atomize
the gas upon application and initiate conduction, thereby removing the
need for a starter and eliminating the warm-up time of the filaments. In
time the solid-state ballast will probably be the unit of choice because of
its quick response, higher efficiency, and lighter weight, but the transition
will take some time. The basic operation will remain the same, however.
Because of the fluorine gas (hence the name fluorescent bulb) and
the mercury in fluorescent lamps, they must be discarded with care. Ask
your local disposal facility where to take the bulbs. Breaking them for
–
Filament starter
Fluorescent bulb
Filaments
+
Blue
Blue
I filament I filament I filament
Windings
(c)
(a)
Filament starter
Laminated core
APPLICATIONS ⏐⏐⏐ 967
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