HID sources, most of these lamps in the 100V to 1000W ratings have an average rated life of 24,000 hrs. Because of this relatively long life, coupled with a slow reduction in lumen output, you should replace them well before reaching their average-rated life. Normal end-of-life (EOL) is a nonstart condition or very low light output caused by blackening of the arc tube from electrode deterioration.
Metal-halide lamp (MH). Operating conditions, such as lamp burning position and normal variations in supply voltage or ballast characteristics, can affect lamp color and light output of MH lamps. Normally, at its end-of-life, an MH lamp won't start because the mix of materials in the arc tube changes. Therefore, the ballast can no longer sustain an arc.
High-pressure-sodium lamp (HPS). Normal end of life indication is on/off cycling, since the aging lamp requires a higher voltage for operation than the ballast can supply. This cycling sequence is normal, but not desirable, since the cycling can damage or destroy the starting circuit and/or ballast. Thus, you should check a cycling HPS fixture without delay. Other conditions that cause cycling include: a loose electrical connection, faulty internal electrical connection to the lamp or at an outdoor installation, and severe fixture vibration, causing lamp voltage to rise above operating limits.
Low-pressure-sodium (LPS). This lamp, which features high efficacy but somewhat limited applications because of its monochromatic yellow color, uses a U shaped arc tube and a two-pin bayonet base. During its burning hours, the lamp's wattage increases. For example, at 20,000 hrs, a 180W lamp draws 247W, so any ampere reading will reflect this increase in wattage consumption because of aging. When troubleshooting, look at the lamp, ballast, capacitor, ignitor (if used), socket, and perhaps the entire fixture for indications of excessive heat.
Let's look at each fixture component separately:
Lamp. Any cracks or holes in a lamp's outer jacket usually indicate a defective lamp. The presence of some form of foreign coating or material on the inside of the lamp's outer jacket can also indicate trouble. This can appear as a light yellow (with an MH lamp) or a silver mirrored appearance (with an HPS lamp). Remember, an HPS lamp will have some normal silver appearance around the lamp base. But, if all, or most, of an HPS lamp's outer jacket has that coating, there's usually a defect. Check the metal parts making up the mount or support for the arc tube for separation or damage. Also observe if the arc tube is cracked or broken. Another procedure is to put an ohmmeter (at the highest setting) across the lamp's center base contact and the base's screw shell. There should be no continuity (it should be open). If the ohmmeter shows continuity, there's a short in the base or mount, and the lamp will not operate. If these procedures don't help you uncover the problem, you can confirm the lamp is defective by putting it in a fixture known to be operational.
Ballast. An HID ballast typically steps up the incoming line voltage to a higher voltage to start the lamp. Thus, a common problem with a multiple-tap ballast can be an incorrect tap connection for the line voltage available. A defective core and coil ballast will usually show signs of its condition, such as darkening of the case or cracked or crumbling insulation, which definitely indicates excessive current flow or excessive heat buildup. Because of its construction, an F-can or encapsulated ballast does not allow you to see the winding. However, these two types often give off a strong odor if they have burned or melted ballast windings. You can make voltage measurements on an HID ballast, similar to a fluorescent ballast, using a multimeter. When you replace a defective ballast, also consider replacing the capacitor, ignitor (if used), and lamp.
Capacitor. Generally, a capacitor fails by either shorting or opening. When a capacitor shorts, it can damage the ballast, lamp, and/or cause excessive current flow, which may cause a breaker to trip. This t