Included
under lighting are incandescent and fluorescent lamps, neon lights, and mercury
vapor, sodium vapor, and metal halide lights. Nominal voltages specified for
lighting are usually 120, 240, and 277 Volts (variations may exist from the
base 120-V value, e.g., 115 and 125 V). All operate with dc or single-phase ac;
the discussion will be in terms of ac, with comments concerning dc operation
where applicable.
Incandescent
Lighting
Incandescent
lamps operate at essentially unity power factor. Their light output drops
considerably at reduced voltage, being some 16 percent less with a 5 percent
lowered voltage, and decreasing at a geometrically faster rate from then on.
They are
also sensitive to sudden rapid voltage variations, producing a noticeable (and
annoying) flicker at variations of as little as 3 Volts (on a 120-V base).
Street lighting of the incandescent type can be operated in a multiple or a
series fashion.
The former
operates as other lighting in a multiple or parallel circuit, while the light
output for the series type depends on the amount of deviation from the standard
value of current flowing through it (usually 6.6, 15, or 20 A); it is sensitive
to variations of as little as 1 percent in the value of the current. The life
of incandescent lamps is considerably reduced at voltages appreciably above
normal.
Fluorescent
and Neon Lighting
Fluorescent
lamps and neon lights operate at power factors of about 50 percent, but usually
have corrective capacitors included so that, for planning purposes, they may
also be considered to operate at 100 percent or unity power factor. Their light
output, per unit input of electrical energy, is considerably greater (25
percent or more) than that of a similarly rated incandescent lamp.
The life of
fluorescent lamps and neon lights is affected by the number of switching
operations they undergo. If fluorescent lamps are used on dc circuits, special
auxiliaries and series resistance must be employed; operation is inferior to
that on ac, with much less light produced per unit of energy and rated life
reduced 20 percent.
Neon lights
are not usually employed on dc circuits. Fluorescent lamps, neon lights,
mercury and sodium vapor, and metal halide lights may, if improperly installed
or when deteriorating, cause radio and TV interference.
High-intensity
Vapor Lighting
Mercury
vapor (high pressure) and sodium vapor (high and low pressure) and metal halide
lights operate at power factors of 70 to 80 percent, but also are associated
with capacitors to raise the effective value to 100 percent.
They are not
as susceptible to voltage variations as are incandescent lamps. Their light output
and life expectancy are greater than those for fluorescent lamps. They may be
employed on dc circuits, but require additional starting auxiliaries.
They are
generally restricted to applications where large amounts of lighting are
desirable, such as on expressways, in large manufacturing areas, or in
photographic work; they are somewhat more expensive than other types and have
the disadvantage of taking some time after being energized before maximum light
output occurs.
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