each end of the lamp. Their bulbs are of
small diameter: T2, T2½, T3, T4, T6, and T8.
Wattages range from 45 W to 2,000 W.
Halogen Infrared (IR) Lamps
0f the energy radiated by standard incandes-
cent and halogen lamps, 85 percent is invis-
ible infrared (heat).Infrared reflecting(IR)
halogen lamps have a thin, infrared-reflec-
tive coating applied to the inner filament
tube that converts some of the infrared
energy to visible light. The coating allows vis-
ible light to pass through the tube wall; the
infrared energy is reflected back onto the
lamp filament, further heating the filament
and producing more visible light for the same
amount of energy.
The operating temperature for the halo-
gen cycle is maintained with less input
power, resulting in increased efficacy: the
efficacy of a standard 1750 lm, 100 W, A-
lamp is 17.5 lm/W; conventional halogen
lamps have efficacies of approximately 20
lm/W; halogen IR lamps have efficacies in
excess of 30 lm/W.
Low-Voltage Lamps
Low-voltage lamps are not of magical con-
struction—they are simply incandescent
and tungsten-halogen lamps that operate
between 6 V and 75 V.
The wattage of all filament lamps is the
product of the voltage delivered at the
socket multiplied by theamperes(current)
flowing through the filament. The lower the
voltage of the lamp of a given wattage, the
higher the amperes and the larger the diam-
eter of the filament wire required to carry it.
The increased diameter of the filament
wire of low-voltage lamps allows for a more
compact filament. The more compact the fil-
ament, the more precise the beam control.
The main advantage of low-voltage lamps is
their precise beam control.
An increase in the diameter of a filament
wire raises the temperature at which it can
be operated without danger of excessive
evaporation. High-wattage lamps, therefore,
are more efficacious than low-wattage
lamps of the same voltage and life rating.
Lower-voltage lamps, because their filament
wire is of greater diameter, are also more
efficient than higher-voltage lamps of the
same wattage; thus, a 120 V lamp (common
in the United States and Canada) is more
efficacious than the 250 V lamps used in
much of the rest of the world.
Low-voltage reflector lamps with narrow
beam-spreads are energy-saving when their
concentrated distribution is used to light
small objects or large objects at great dis-
tances because light is confined to the
lighted object without spilling beyond it.
Where wider beams are required, low-volt-
age lamps are often less efficient than stan-
dard lamps.
Low-voltage operation also means that
the standard building current of 115 V to
125 V must be stepped down by the use of a
transformer. Low-voltage luminaires with
integral transformers are often larger, bulk-
ier, and more expensive than line-voltage
equipment.
The low-voltage lamps commonly used
for architectural applications operate at 12
V. They include PAR, AR, and MR lamps.
Low-voltage PAR lamps are manufactured in
the same way as line-voltage PAR lamps; the
shape and diameter of the lamps may differ,
and the bases are always different to avoid
wrong electrical connection (figure 6.11).
Many low-voltage PAR lamps are
equipped with filament shields to minimize
the stray light that comes directly from the
filament. As a result, the lamps emit only the
controlled beam from the reflector. These fil-
ament shields have the added benefit of pro-
viding glare control by preventing view of the
filament.INCANDESCENT LAMPS