Lamp Construction of Dependable's Mercury Vapor

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 800C. Under actual operating conditions, arc tube temperatures between 600C and 700C 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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