Understanding how fluorescent and HID lamps work makes problem solving and corrective maintenance easier.
If you work with arc discharge lamps, you know troubleshooting can be tricky. It never fails: Your ingenious idea that solved yesterday's problem doesn't work today. So how do you predict the unpredictable? You must get to know these fluorescent and high-intensity-discharge (HID) light sources inside and out to truly understand their behavior.
Arc discharge lamps produce light by an electric arc struck between two main electrodes or cathodes. With few exceptions, they must operate with a ballast, designed to provide the proper starting and operating voltage for the lamp. A ballast changes the voltage of power supply to what the lamp needs to start reliably (provide the open circuit voltage), regulate the current (ampere flow) to the lamp, and maintain the proper voltage to the lamp during operation. Usually, you know there's a problem with a discharge fixture when the lamp (or lamps) shows one the following conditions: nonstart, cycle on and off, extra bright light output, or low light output. Any one of these is reason enough to deenergize the fixture and take a closer look. To help you troubleshoot, we'll look at the fluorescent source first and then the HID source.
Fluorescent lamp characteristics. Fluorescent lamps can be divided into the rapid-start and instant-start type (Slimline lamps that do not have cathode heating).
Rapid-start (RS), high output (HO), and 1500mA T12 lamps all have similar characteristics. They depend on the proper heating of the cathodes to start up and operate properly.
Slimline lamps do not use cathode heating. They use the ballast open circuit voltage (which can be about three times the normal lamp operating supply voltage) to start operation.
When fluorescent lamps don't operate, the ballast may not be the culprit. Therefore, before replacing the ballast, examine all components.
Change or check lamps to ensure proper operation. As you remove them, examine sockets to ensure proper and positive contact with lamp pins.
If you used starters, check and replace each as necessary.
Examine the ballast leads to make sure the connection matches the diagram on the ballast label.
Examine and test the ballast. Leaking compound (except for a normal small amount at the lead holes), cracking or brittle insulation, or discoloration on the can may indicate the ballast (especially an electromagnetic type) is approaching, or has reached, the end of its life.
The Table (in the original article) offers general instructions for troubleshooting when fluorescent lamps do not start.
At the outset, we'll discuss two specific problems found in any type of fluorescent system. We call the first cycling. The National Electrical Code (NEC) requires most indoor ballasts to have a cutout device that protects them from overheating. If high ambient conditions cause the ballast to overheat, the thermal protection device's switch disconnects it from the power supply; if the temperature at the ballast is reduced, the cutout device closes, reactivating the ballast, thus restarting the lamps. If such a cycling condition persists, you must find the cause of the high temperature and correct it.
We call the second condition swirling, where the light appears to swirl or spiral inside the tube during operation. This normal occurrence can last for a few hours with some new lamps when first energized. However, a cold ambient temperature or low input voltage can also cause the problem.
Rapid-start (RS) systems. To measure the starting voltage of an RS ballast, connect a voltmeter between the highest reading Red lead and Blue lead with the lamp removed. See Fig. 2 (in the original article). Consider the following example: For an F 40 T12 two-lamp ballast, the minimum starting voltage is 256V. The minimum starting voltage for F96T12HO two lamp ballast is 466V. For a F96T12VHO ballast, it's 470V. All numbers are for minimum ambient temperature of 50DegrF. You should find these open circuit voltages on the ballast's label. (Note: Electro