HIDThis guide is prepared to assist
electricians with normal routine maintenance and to help them understand the operation of
different lamp sources and electrical systems.
Caution: High voltages, currents, and temperatures
are required to operate gas discharge lamps. Shock and burn hazards exist, and testing or
evaluating fixtures or compo-nents should be done by qualified individ-uals only.
Light Sources:
Fluorescent
Mercury Vapor (MV)
Metal Halide (MH)
High Pressure Sodium (HPS)
Lamps
Fluorescent lamps come in many sizes, shapes and colors.
This lamp source can provide numerous advantages, depending on the needs and requirements
of end users. These lamps are generally used when low mounting heights and quiet operation
are required. Note that many new, more efficient lamps and electronic ballasts offer the
customer many energy saving opportunities.
Mercury Vapor lamps were the first to be developed in the
family of high intensity discharge (HID) lamps. Their advantage is that they offer long
life. Their disadvantages are poor color rendition, poor lumen maintenance, and low
efficiency.
MH lamps are similar to MV lamps in design and operation.
Their lumen output is double that of MV lamps of the same wattage. MH lamps are used in
installations that require high efficiency, and white light. Lamp life historically has
been less than MV and HPS, however new MH systems are now changing this by providing
excellent life, lumen maintenance and color control.
A. HPS lamps
offer long life and more lumens per watt than MV or MH sources. HPS lamps emit a pale
amber color compared to other whiter light sources. Energy savings is the main HPS
advantage. New high-xenon HPS lamps offer even higher LPW, longer life and improved lumen
maintenance.
Ballasts
All HID light sources require some form of ballast because:
Most require a starting voltage that is higher than the
line voltage.
They all have a characteristic known as negative
resistance. This means that once the arc is initiated, the lamp’s resistance
continually decreases as current increases. For all practical purposes, the lamp becomes a
short circuit. The ballast limits and controls the current wave form through the lamp.
They provide voltage transformation to allow the use of many line voltages.
There are many different types of ballasts used with
different lamps. Within a lamp type, ballasts vary in lamp operating wattage and
regulation caused by changes in line voltage and lamp voltage. Better regulation and
control normally results in higher initial cost, but may greatly improve operating
characteristics and overall performance.
Capacitors
Capacitors are used for power factor correction or as
current regulation devices which provide the control necessary to ensure proper lamp and
ballast operation. Different wattages, voltages, and ballast types require a variety of
different capacitors. The ballast ID label specifies the microfarad and voltage rating
required for proper operation. If the capacitor is incorrectly wired, improper operation
of the fixture as well as other component failures could result.
Ignitors/Starters
These devices are utilized to provide the proper voltage
and energy to start the lamp. They are predominantly used with HPS lamps as well as some
Metal Halide and Fluorescent systems.
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