lamp. You will read infinity. Remember, infinity
means that the circuit is good, and continuity means a
short. Now, connect the ohmmeter between the neutral
and the lead going to the middle lamp. The reading will
show continuity, indicating the short is beyond Point A.
You should leave Point A open at this time and continue
on to the middle lamp.
Disconnect Point B and take the same readings that
you took at the first light. From these tests you can
determine that the circuit between the first and middle
lamp is all right (infinity reading), and the trouble must
be between the second and third lamp. By checking
closely at the middle junction box, you can probably see
charred or frayed wires indicating the problem. You
may need to continue your check to Point C. Use the
same procedure as with the other lamp, and find the
trouble between Points A and C.
After installing the switches needed to control the
lighting, you need to mount the light fixture itself. Each
lighting installation is designed to produce a specific
level of illumination adequate for those working in the
area. The amount of illumination initially provided
starts to decline almost as soon as it is put in operation.
This reduction is caused by dirt on the lamps and
luminaries, a decrease in lamp lumen output, and dirt on
the room walls and ceilings. Illumination should be
sufficient to eliminate eyestrain, support a high level of
production, and promote safety and employee morale.
Lighting fixtures are designed for a particular lamp
size and type. Many fixtures, however, were installed in
military buildings long before the manufacturers started
producing higher and higher wattage lamps in ever
smaller envelopes. Consequently, it is possible to use
much higher wattage lamps than the fixture or the
circuit can handle adequately.
Excessive heat of higher wattage lamps can
damage the sockets, increase failure rate, and
overload the circuits. Personnel are cautioned
to use only the lamp size (in watts)
recommended for the fixture, rather than a
higher wattage lamp that may physically fit.
Incandescent lamps come in a variety of voltage
ratings. For most applications, the lamp voltage rating
nearest the available line voltage should be selected.
Under this condition, the lamp will produce its rated
values of life, watts, and light output. Many
incandescent lamps are available with life ratings
considerably in excess of ordinary general service
lamps. Some have ratings of 5,000 hours or more, and
some even are guaranteed to burn for 5 years. General
use of these lamps is not recommended because the
initial cost is comparatively high and the extended life is
gained by reducing the light output. There are,
however, a few areas where it is necessary to use bulbs
with a long life. Typical locations include high-ceiling
auditoriums, exit lights, stairwells, and marker lights on
towers or fire alarm boxes. For these areas, do not use a
special rated lamp. Do use an ordinary general service
lamp whose voltage rating is higher than the circuit
voltage; for example, 130-volt or higher lamps for 120-
volt circuits. When you are operating the lamp below its
rated voltage, the life is increased at a sacrifice in light
output. For general use, the lamp voltage rating nearest
the available line voltage should be used.
Many kinds of incandescent lamps are especially
designed for placement in a variety of situations; for
example, under severe physical conditions (such as
vibration or extreme temperatures), in inaccessible
locations, or when special lighting effects are desired.
Some of these types of incandescent lamps and their
uses are as follows:
INSIDE-FROSTED LAMPS are used in most
fixtures designed for incandescent lamps. The frosted
finish reduces lamp brightness and glare.
CLEAR LAMPS are used in fixtures where
control of the light is required (such as in reflectors
having polished reflecting surfaces and in enclosed
globes or reflectors of prismatic glass), particularly
where concentrated light control is required, as in high,
Reflector equipment of the diffusing globe type,
where the lamp protrudes through the bottom of the
fixture, requires WHITE BOWL LAMPS. The white
bowl reduces the surface brightness and glare from the
SILVERED-BOWL LAMPS are used principally
for indirect lighting and in reflector equipment. The
fixture parts should not touch the lamp as the thermal
expansion may cause the bulb to crack and fail
REFLECTOR LAMPS with the reflecting
surface inside the lamp are, in effect, a fixture in
themselves. A collection of dust and dirt on the exterior
of the lamps can cause them to lose their effectiveness.