Page 254 - Electromechanical Devices and Components Illustrated Sourcebook

216 Electromechanical Devices & Components Illustrated Sourcebook

Tube Base Terminals
Upper Electrode

Upper Electrode
Argon Gas Molybdenum Plates
Quartz Arc Tube
Vacuum Jacket Bulb
Glass Bulb Supporting Leads Sodium-Mercury Quartz Arc Tube
Filament Support Leads
Mercury Filaments
Lower Electrode
Lower Electrode
Starting Resistor

Figure 12-19 High-Pressure Sodium Vapor Lamp
Admedium Screw Base

necessary to provide insulation for the high temperatures at
Center Terminal which these bulbs must operate. The quartz tube contains a
Figure 12-17 Commercial Mercury Vapor Lamp small amount of sodium and neon gas. There are two fila-
ments mounted on either end of the tube. Starting the lamp
is similar to starting a fluorescent unit. The two filaments are
heated, generating electron flow and heat. The heat vapor-
izes the sodium and, after a predetermined start period, the
filaments are turned off, high voltage is applied to the fila-
ments and the plasma initiate. The small molybdenum plates
that are backing the filaments are intended to protect the fil-
aments by carrying the bulk of the extreme heat that the
Lamp lamp generates during operation. It takes about 30 minutes
for a sodium vapor lamp to come up to full operating tem-
perature, so it is important that the lamps are used in appli-
cations where a warm-up period is acceptable. One other
note, these lamps are referred to as high pressure because
Autotransformer
the internal pressure of the quartz tube is at several atmo-
spheres during operation.
Power
Standard Lamp Bases
Figure 12-18 Mercury Vapor Lamp
There are a variety of standard lamp bases that are commonly
Power Supply
available when selecting a light bulb. Common sense will dic-
tate most of these choices, as an example, most household
lighting utilizes a medium screw base lamp while automo-
established, the low resistance pulls the transformer’s voltage biles typically use a three lug pattern. It doesn’t make much
down to the operational voltage. sense to buck the norm and place a bulb into a service for
which it isn’t designed.
Figure 12-20 shows the standard screw bases that are com-
High-Pressure Sodium Vapor Lamps monly used for incandescent lamps. The medium is the most
common size, used for light bulbs in the 25 through 150 watt
Sodium vapor lamps have become the lamp of choice for range. Intermediate and candelabra sizes are commonly used
highway lighting. These are the lights we see on our freeways for decorative lamps, Christmas lights, indicator lamps, and
that produce the golden-yellow light. This spectrum of light is nightlights. The miniature is found in flashlights, indicator
more comfortable to the eye, producing softer shadows and applications, and model building. The medium skirt is typi-
less glare. cally used on lamps that are used in outdoor fixtures, such as
Figure 12-19 shows a typical high-pressure sodium vapor flood lights. Admedium size is mostly used for higher-wattage
lamp. The lamp consists of a quartz tube mounted in the cen- lamps and mercury vapor lamps. The mogul base is used in
ter of a vacuum jacketed bulb. The vacuum jacket bulb is industrial and high-wattage applications.