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HID – The Burning Question … Base Up, Base Down or Horizontal: What’s the Deal ... - page 3 / 4





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approximately 1100°C. The arc tube and outer bulb may unexpectedly rupture due to internal causes or external factors such as a system failure or misapplication.

An arc tube rupture can burst and shatter the outer glass bulb resulting in the discharge of glass fragments and extremely hot quartz particles (as high as 1100°C). There is a risk of personal injury, property damage, burns and fire. Because of this, some Metal Halide lamps are “position-sensitive” and must only be operated in specified burning positions using compatible electrical equipment and installation in suitable fixture types as prescribed in the LET “Lamp Enclosure Type” designation field of the manufacturer’s catalog. For more information about the use of Metal Halide lamps, see NEMA’s "Best Practices for Metal Halide Lighting Systems, Plus Questions and Answers about Lamp Ruptures in Metal Halide Lighting Systems," NEMA LSD 25-2004.

Note: HPS and mercury are not position-sensitive and may be operated in any burning position.

EFFECTS FROM IMPROPER ORIENTATION The Arc tube may become bulged or swollen. After extended operating hours some bulging is normal, especially in the off-vertical burning position. If a lamp bulges prematurely, this condition may indicate the lamp is operating at a higher-than-rated wattage due to miswiring, using the wrong lamp on specific ballast or the fixture optical system is directing too much heat onto the arc tube. This problem must be corrected or else the lamp may unexpectedly shatter.

POTENTIAL FOR NON-PASSIVE FAILURE Normal end-of-life (EOL) of these lamps is a “non-start” condition, resulting from a loss of sodium from the arc that changes the electrical characteristic so that the ballast can no longer sustain the lamp. The 400- and 1,000-watt lamps, when burned vertical ± 15°, usually have a passive EOL failure mode. Other wattages, regardless of burning position, and the 400- and 1000-watt lamps when burned in other positions, can fail in a non-passive manner, and the outer bulb may shatter. Therefore, they should be operated only in an enclosed fixture that will contain the lamp if it shatters. Color at EOL will usually be warmer (pinker) than a new lamp, since the arc tube has blackened due to electrode deterioration. This can cause a change in the thermal balance within the arc tube that results in this color change.

ORIENTATION IN OPEN FIXTURES For lamps operated in the vertical position that are not designated “Enclosed Fixtures Only

  • Type E,” lamps may be used in an open or enclosed lighting fixture depending upon the

application and operating environment. For example, if the lamp is located near combustible material or in an area unoccupied for extended periods, an enclosed fixture that can contain fragments of hot quartz or glass is recommended.

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