HID
lamps are actually made with two bulbs: an inner bulb (the arc
tube) and an outer bulb. The purpose of the outer bulb is to keep
air out of the inside portion of the lamp and to provide an
insulated atmosphere around the arc tube in order to maintain the
proper operating temperature required for high efficiency under
normal operating conditions. The outer bulb also absorbs UV energy
generated by the arc tube.
The inner bulb, commonly
called the arc tube or 'burner', is the light producing component
of the lamp. It contains metallic and gaseous vapors and the
electrodes necessary to generate the arc of electrons.
The features described below are characteristics of SERVICE
GUARANTEED mercury vapor, metal halide and high pressure sodium
lamps. Low pressure sodium, which has some unique characteristics,
will be discussed later.
1.
Graphite Base- The date coded graphite base will not "freeze" or
corrode in the socket even after years of installation. A special
silicone based cement forms a bond with the glass to insure
against separation of the base from the glass bulb.
2. Unitized Mount Frame -
The mount frame assembly provides a cushion support for the arc
tube and also provides a means of getting electricity to the arc
tube . T minimum number of welds in our design means fewer weak
points that can break for a more reliable lamp that lasts longer
under vibration.
3. Starter Electrode/Resistor -
Designed and constructed to withstand shock and vibration, the
starter assembly is built to take the high ballast voltage
necessary to insure reliable starting. (Starting electrodes and
resistors are not required in high pressure sodium lamps)
4. Arc Tube Seal - A
on-piece full-press construction assures optimum uniformity and
lamp performance. HPS lamps have a ceramic to metal seal. A unique
system for sealing the end of the arc tube dissipates heat from
the electrodes and lengthens lamp life.
5. Arc Tube - The arc tube
of the SERVICE GUARANTEED mercury vapor and metal halide lamp is
made of fused silica rather than standard heat resistance glass.
The advantage of a fused silica arc tubes are it can withstand
more heat than glass. The inner burner of the SERVICE GUARANTEED
lamp can be operated at temperatures as high as 800°C. Under
actual operating conditions, arc tube temperatures between 600°C
and 700°C are experienced. It permits operation in any
burning position.
It allows for a smaller, brighter source
of light
6. Back wound Electrodes -
Inside the arc tube are two main electrodes (and the starting
electrode, discussed above) which make up the heart of an HID
lamp. Lumen maintenance, starting and life are all dependent on
the construction and quality of the electrodes. Our unique back
wound electrodes are designed to trap the emissive coat in, in
which all electrodes are dipped, which inhibits the sputtering
process. By preventing escape of the emission material, the arc
tube remains clean thus providing maximum light output throughout
the life of the lamp.
7. Phosphor Coating - Some
HID bulbs are coated on the inside for improved color and reduced
surface brightness.
8. Outer Bulb - The outer
bulb is made of a hard glass to withstand thermal shock caused by
rain or snow.
9.
Safety Mercury Vapor Lamps - Light in the ultraviolet spectrum is
generated in the mercury vapor arc tube. Normally, the outer bulb
will absorb the UV waves which can cause skin irritations, (sun
burning) and eye irritation. If the outer envelope is broken, the
arc tube may continue to operate creating the possibility of
ultraviolet exposure. Safety mercury vapor lamps contain an
oxidizable tungsten fuse that is placed in series with the arc
tube. when the bulb is fractured, outside air enters the bulb.
The fuse burns in the air and fails. when the fuse fails, the arc
tube will stop operating and ultraviolet radiation will no longer
be emitted.
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