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Lamp Types
The fundamental difference between
lamp types is the way the
filament, is coiled and supported.
The tungsten wire is very fine
with a diameter less than human
hair and the overall length of
100W filament is nearly 1.2m so
coiling is necessary to produce a
sensible sized lamp.
Figure 4.6. Single and
Coiled Coil detail.
Figure 4.7. Coiled Coil
supports.
Figure 4.8. Rough Service
supports.
Filament Construction
Coiled Coil is the most common for
household gls lamps, see Figure
4.6 and 4.7. The arrangement
use the minimum numbers of
filament supports so little heat
is conducted away from the
filament. With 220V to 250V
filaments it produces a compact
configuration so that the heat is
retained within the filament space
and optimum light output is
achieved. Also the filament forms
a small area for optical control
and efficient reflector systems do
not have to be excessively large
and expensive.
Single Coil filaments are made for
both high and low wattage lamps.
The extra numbers of supports are
of value where vibration is likely
to be encountered, which can
fracture the thin tungsten
filament.
Both Coiled Coil and Single Coil
filaments have all their supports
in one plane so they function best
when the lamp is either cap up or
cap down. If the lamp is used
horizontally there is less support
and filament sag can occur with a
reduction in lamp life.
Where lamps are known to be used
in various positions then a Rough
Service lamp is used. The supports
are not in a single plane but the
filament is in a zigzag pattern so
that good support exists
regardless of the lamp
orientation. See Figure 4.8.
REFLECTOR lamps provide a
directional beam of light as shown
in Figure 4.9. Both spot
and flood beam spreads are
available. The shape of the bulb,
the sides of which are coated with
vaporised aluminium to form a
reflecting surface, determines the
spread of the beam. The face of
the bulb may be frosted to provide
diffusion of the light beam.
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