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 TM 5-684/NAVFAC MO-200/AFJMAN 32-1082
aviation lighting. Tungsten-halogen lamps are often
absorb unwanted light. Any degradation of these
used for recreational floodlighting, where good color
items resulting from accumulated dirt or fixture
rendition is necessary.
damage will result in a less efficient lighting instal-
lation.
b. Electric-discharge lamps. Electric (or gaseous
b. Component support assembly. The assembly
discharge lamps) include mercury-vapor, metal-
halide, and high- and low-pressure sodium lamps.
provides the mechanical support for lampholders,
They differ in the gas or vapor used, which is either
sockets, ballasts, controls, reflectors, refractors, en-
mercury, or mercury with halide salts, or sodium, at
closures, mounting components, and other items
different pressures. Most outdoor public way light-
needed to ensure the lamp provides the perfor-
mance needed.
ing installations today use high-pressure sodium
lamps. Most older mercury vapor luminaires are
c. Circuit controls. Photo cells are the only circuit
being replaced with high-pressure sodium lumi-
controls that are provided integrally with the
naires because of the energy savings. Metal-halide
luminaire. They are described in paragraph 6-8.
lamps may be used for recreational and protective
6-7. Luminaire maintenance.
lighting systems, because their superior color rendi-
tion outweighs their lower lamp life and lumen out-
Luminaire maintenance given herein is for high-
put. Low-pressure sodium lamps, though they have
pressure sodium (HPS) lamps which will most often
a greater lumen output, also have a monochromatic
be found in roadway and recreational lighting.
color rendition and a lower lamp life and are rarely
Maintenance of other lamps should follow the same
used for outdoor lighting installations on military
philosophy. Luminaire maintenance consists of
facilities. All lamps require ballasts for correct op-
cleaning, lamp replacement, and troubleshooting of
eration.
components when other problems are indicated.
c. Fluorescent lamps. A fluorescent lamp utilizes
a mercury vapor, but the inside of the bulb has a
erally the average illumination delivered at the de-
thin coating of phosphor which glows or fluoresces
sign point when the illuminating source is at its
when struck by the electrons flowing through the
lowest output and the luminaire is in its dirtiest
mercury vapor. The amount of light emitted is less
--
condition. This requirement determines the mainte-
than for electric discharge lamps, and only a limited
nance frequency.
control is possible because of their tubular shape.
(1) Lamp depreciation. The lumen output of
They may be used for lighted roadway, traffic, or
HPS lamps will decrease to 80 percent of its initial
airfield indication signs. All lamps require ballasts
value at about 80 percent of its rated life. The lamp
for correct operation, and some types require sepa-
should then be replaced to maintain design
rate starters to provide the heat necessary for the
footcandle levels. Rated lamp life is defined as ap-
electron emission to start.
proximately the time for half of the lamps to fail.
Using a value of 24,000 hours for 80 percent of lamp
6-6. Luminaire components.
life, and 4,000 hours of burning time per year, re-
In addition to lamp or lamp/ballast combination, the
sults in a theoretical 6-year life for half the lamps.
components of a luminaire include its optical con-
On this basis, consider group replacement every 4
years. Premature outages can probably be held to
trols, its component support assembly, and possibly,
approximately 10 percent if group replacement is
circuit controls.
made before the lamps approach the accelerated
a. Optical controls. Optical controls are used to
point on their mortality curve. The few lamps which
provide the light distribution pattern most appro-
do fail should be replaced promptly.
priate to the outdoor lighting requirement. One type
(2) Luminaire depreciation. Dirt on lamps, re-
of control is a reflector which uses a parabolic, ellip-
flectors, and refractors is another cause of de-
soidal, or hyperbolic contoured surface with a
creased lumen output. A cleaning schedule should
specular, spread, diffuse, or compound finish to re-
be set up on an annual basis, that under normal
direct light from a lamp into the desired pattern.
operating conditions, dirt will not contribute more
Another type of control is a refractor which uses a
than 15 percent to the lighting depreciation. Clean-
different medium to bend the light. Refractors can
ing recommendations for average dirt conditions
provide a variety of light distributions, using pris-
range from every 2 to 3 months up to a 2-year
matic or lens type refractors of glass or plastic.
schedule for inspection, cleaning, and washing.
Other optical control methods use glass or plastic
b. Cleaning. Cleaning can be done from lift
materials to scatter light or control brightness. Lou-
vers or shields are used to mask a source or to
trucks using a one- or two-man crew. The crew
6-2
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