FAQ

Q: Normal End of Lamp Life
A: Normal end of life is important to understand for troubleshooting. It occurs when the lamp has aged to the point that the arc can no longer be sustained. End of life can be induced prematurely when lamps are operated at improper voltages, temperatures and positions. Mercury and metal halide lamps tend to emit low light output at end of life and starting will become intermittent. There will also be significant blackening on the arc tube located at the center of the lamp. High pressure sodium lamps retain their light output at the end of life, however, starting becomes intermittent at first and then impossible. There will be some blackening on the end of the arc tube located in the center of the lamp. Verify average rated lamp life as published by the lamp manufacturer and compare it to the actual life of the lamps in the system. Remember that the average rated life is not the same as the minimum life expectancy. The average rated life means that for a population of lamps, the average lamp lasted this long. When a system of lamps installed at the same time reaches the average rated life, we can expect half of the population of lamps to have failed. It is always important to be aware of the operation of the system when evaluating lamp life. For example, is the system operated round the clock either intentionally or as the result of faulty controls?

Q: Lamps Will Not Start
A:

• 1. Check to see if lamp is loose in the socket. Check for arcing (blackening) at the center contact button and retighten lamp until it is properly seated. Tightening too much may cause lamp breakage.
• 2. Check to see if lamp has failed or is damaged. Visually inspect for loose, broken internal parts or broken bulb wall. Visually inspect for separation of the lamp base. Check for looseness or for significant discoloration of the bulb wall near the base. Test the lamp in an adjacent fixture that is operating properly.
• 3. Check to assure that the voltage at the fixture is not too low. Check the nameplate rating for the ballast. The voltage should be within 5% for reactor and high reactance ballasts, and within 10% for all others

Q: Lamp Cycling (starting and shutting off repeatedly)
A:

• 1. Lamp cycling is a common end of life failure mode for high pressure sodium lamps.
• 2. Check the photocell (if applicable):
  If a photocell is used to switch the fixture, cover the photocell window or eye completely with black electrical tape and check for proper operation. If the cycling STOPS, re-aim the photocell (or the fixture) to reduce fixture light spill onto the photocell eye. If the cycling CONTINUES, replace the photocell with a shortening cap if available or bypass the photocell completely in the circuit temporarily. If the lamp remains on, the photocell is defective. If the cycling STILL CONTINUES, the lamp is probably bad.
• 3. Check the capacitor:
  Verify the capacitor has the correct microfarad (uF) value as specified on the ballast. Inspect the capacitor for a swollen or ruptured case. Disconnect the capacitor and discharge it by shorting across its terminals with a piece of insulated wire. Use an analog ohmmeter set on its highest scale to test resistance. If the resistance starts low and gradually increases, the capacitor is good. Any other reading indicates either an open or short circuit condition and the capacitor is bad.
• 4. Check the ballast:
  If it is an older system, it could be simply the normal end of ballast life. Replace the ballast, capacitor (if present) and ignitor (if present). If the ballast is located in an extremely high ambient temperature, it can overheat the ballast or other parts. Check for discoloration of the ballast or other parts. Also check for failed capacitor (see above). Check the ballast open circuit voltage. (See Electrical Tests)

Q: Off Color (Color Shift) Lamp Or Low Light Output
A:

• 1. Install a known good lamp from a similar fixture.
  If lamp is near its normal end of life, low-light output may be noticeable. Color shift will occur as a lamp ages. The color of the light source (called chromacity) tends to vary somewhat from lamp to lamp in all metal halide lamps. However, because the chromacity changes with time as the lamp ages, differences become most noticeable when new lamps are introduced into an aging group of lamps. Spot replacement of older lamps is the most common cause of dissatisfaction with lamp color. GROUP RELAMPING IS HIGHLY RECOMMENDED. Color differences in the light source can also be exaggerated when lamps of different types and manufacturers are used adjacent to one another. Variations in the thickness of the phosophor coating of coated lamps can also cause color variations. Lamp color is also affected by wattage variations, which can be as wide as +/- 7.5% according to ANSI standards. Interchanging different lamps may minimize apparent color differences. Color difference in walls, ceilings, office partitions, and floors, as well as other sources of illumination can affect apparent lamp color.
• 2. Check lamp specifications for specific base orientation: "base up" or "base down". Certain metal halide lamps have a special position-oriented mogul base which must be utilized with the corresponding position-oriented socket. Use the specified lamp only in the correct position. If this is not done, the arc tube will not be correctly oriented and low-light output or possible lamp failure can result.
• 3. Clean the reflector, refractor, and/or lens to make sure the transmitting medium is not distorting the fixtures light output.
• 4. Inspect the capacitor for a swollen or ruptured case.
• 5. Check the ballast open circuit voltage
• 6. Check for a low-supply voltage condition.

Q: Short Lamp Life
A:

• 1. Verify the correct ballast type and wattage, and correct capacitor value.
• 2. Check the input voltage and verify that it does not exceed 10% ballast input voltage shown on the label.
• 3. Inspect the capacitor for a swollen or ruptured case.
• 4. Check the lamp specification for "base up" or "base down" position specifics. Use the specified lamp only in the current orientation.
• 5. Replace with a known good lamp.

Q: Lamp Starts Slowly (Arc Does Not Strike When Switch Is Turned On.)
A: A hard starter is a lamp which will not start rapidly. It may glow for extended periods of time destroying cathodes. It should be replaced after checking voltage and ballast.

Q: Fuses Blow or Circuit Breakers or Circuit Breakers Open On Lamp Start Up
A: Overloaded Circuit - Rewire to accommodate starting current of lamp/ballast combination.

High Momentary Transient Current - Can be caused by reactor or autotransformer ballasts which draw high initial currents. Use current protective devices incorporating time delay elements. If these fail, change ballast as its characteristics will affect lamp life.