Introduction to HID Lighting
High Intensity Discharge
(HID) is a broad term used to describe any lighting system using a gaseous discharge arc lamp in which the gas-filled arc tube operates at several times normal atmospheric pressure compared to the near vacuum conditions in fluorescent lamps. The various types of HID lamps are categorized and named by the type of gas contained within the arc tube.
The electrical arc produced between the two main electrodes of an HID lamp is much like a runaway short circuit which can be sustained indefinitely. Once sufficient voltage is present, the gases within the arc tube are “ionized” to where they will conduct the arc current. Arc formation is not an immediate process. It can take several seconds for the arc to be established, and several minutes until full light output can be reached.
HID lamps are negative impedance devices. This means that unless controlled, the current would continue to increase, causing the lamp to fail almost instantly after starting. For this reason, a ballast, which is a current-limiting device, must be used with every HID lamp. The ballast serves three functions. It provides the proper starting voltage to establish the arc. Second, it supplies the proper voltage to operate the lamp. Third, the ballast limits the lamp current to a level prescribed by the lamp manufacturer for the particular type of lamp being used. Ballasts must always be matched to the particular lamp type, wattage, and line voltage being used. Never use a ballast for any lamp, installation or purpose other than that for which it has been specifically designed.
The ionization voltage of all HID lamps increases greatly when the lamp is hot. If power to the lamp is interrupted, the lamp must be allowed to cool for a time, usually several minutes, before the arc can be reestablished and normal operation resumed. For this reason, some ballasts are available with a tap to operate a standby, or auxiliary, incandescent lamp through an appropriate interface device. The 120-volt lead on dual-,tri-, and multi-voltage ballasts can be used as a tap for standby lighting when the ballast is supplied by a higher line voltage. For some ballast-lamp combinations, an instant restrike starter is available.
Suggestions for HID Fixture Maintenance
Proper maintenance of any lighting system is essential to maintain levels of illumination necessary for productivity, merchandising, visual comfort, safety, and security. If an individual component fails and is allowed to remain in the lighting system, costly damage to other components can result. Major repairs can often be avoided by simple maintenance procedures and timely attention to small problems, such as replacing burned-out lamps.
Preventing a problem from occurring is more desirable and economical than fixing it later. A scheduled program of preventive maintenance can save money while maintaining productivity and safety. By using the following maintenance strategies, the ballast will have a longer, more trouble-free life. There are many lighting maintenance contractors and electrical contractors who can economically perform a scheduled maintenance program.
Lamps should be replaced as a group at scheduled periodic intervals, based on rated life, minimum acceptable lighting levels, and system operation cost. Your lamp supplier has additional information available regarding lamp maintenance procedures.
Lamps, reflectors, and lenses should be cleaned periodically. Be sure to follow the recommendations of the fixture and/or reflector manufacturer.
In addition, to obtain normal ballast life and maximum efficiency from an HID lighting installation, fixtures should periodically be inspected for:
- Lamps cycling on and off
- Heavy lamp discoloration
- Dim lamps
- Slow-starting lamps
- Inoperative lamps
- Dust and dirt
The significance and correction of these conditions can vary with the type of lamp and ballast used; these are covered in greater detail in this guide.
Lamps should be checked to be sure the proper lamp type is being used, according to the information on the label of the installed ballast. Many lamp types currently offered, such as metal halide and high pressure sodium lamps, are physically interchangeable, but not electrically interchangeable.
Line voltage should be checked at the fixture and compared with the ballast rating to be sure it is within the prescribed limits. (See Appendix E.)
A high pressure sodium lamp cycling on and off usually indicates the lamp has reached the end of its normal life. (See Appendix B.)
Lamps cycling on and off with an encased & potted ballast, or other ballast which contains thermal protection, may be a warning that the ballast is operating at too high a temperature, causing the automatic resetting thermal protector to deactivate the ballast when the temperature limit is exceeded. (See Appendix G.)
Make certain that the polarity is correct. (See Appendix E.)
Be sure the fixture, ballast, capacitor and starter are properly grounded. (See Appendix E.)
Ballast, capacitor and starter replacement, as well as lighting maintenance, presents the possibility of exposure to potentially hazardous voltages and should be performed only by qualified personnel. All installation, inspection and maintenance should be performed only with the entire circuit power to the fixture or equipment turned off.
All ballasts, components and fixtures must be installed and operated in compliance with the National Electrical Code, requirements of Underwriters Laboratories, Inc., and all applicable codes and regulations. This includes, but is not limited to, proper grounding of ballasts, components and fixtures as well as prescribed branch and total circuit protection.
This concise guide provides a logical sequence and procedures for troubleshooting and correcting the most commonly encountered problems in a typical HID lighting system. There are many specialized ballasts, lamps, fixtures, and lighting controls which are not specifically addressed. The troubleshooter should always check for special conditions which might exist in an installation, creating an exception to the rules or a potential safety hazard.
Protect the Ballast
A ballast, like any electrical device, generates heat. To ensure maximum ballast life, it is imperative that operating temperatures be kept low. Burned-out or failing lamps, or high temperatures in or around the fixture, can cause the ballast to overheat, resulting in premature failure. For more information regarding heat’s effect on ballast life, in addition to recommendations for maximizing ballast life and performance, consult Universal Lighting Technologies’ catalogs.
For Additional Assistance
If additional troubleshooting assistance is required, or you have any questions regarding your lighting system, we’re ready to help! Call Universal Lighting Technologies’ Technical Engineering Service™ Department at 1-800-BALLAST.