High-Intensity Discharge (HID) Lighting

HID lighting systems are being used more and more for two reasons: longer bulb life and greater energy efficiency. Longer bulb life results in lower maintenance (relamping) costs. Greater energy efficiency, simply stated, means more light (lumens) per watt of energy. As a comparison between incandescent bulbs and HID bulbs, an incandescent bulb that consumes 575 watts provides 10,000 lumens and has a lifespan of 1,200 hours, while a metal halide lamp at 400 watts provides 32,000 lumens and has a lamp life of 10,500 hours. A high-pressure sodium HID bulb of 400 watts consumption provides 42,000 lumens with a life of 6,000 hours. As you can see from these examples, the HID lamps far surpass the older incandescent lamps in light bulb life and efficiency. The economic life of the HID bulbs ranges from 6,000 to 20,000 hours. Lamp temperatures should be maintained below 210F at the base and should not exceed 400F outer bulb temperature. Specific voltages are required for these lamps and should not vary more than 5 percent above or below this specified rating. Low voltages will cause the lamps to go out.

Normally they will not restart until the internal vapor pressure is reduced to a point at which the arc can be restarted. This time may vary from 4 to 8 minutes. The existing conditions will govern this time. Where extremely cold conditions exist, such as in streetlight or floodlight systems in winter temperatures, specially designed ballasts (transformers) are installed to provide a higher open-circuit voltage to aid in starting the lamps.

You should remember that all HID lights produce a stroboscopic effect and, when possible, adjacent lamps should be powered from different phases to reduce the results of this effect.

If a system is simply being upgraded by changing out incandescents for HID lamps, the present wiring is probably adequate to handle the change since the HID lamp requires less power than the older incandescent system. Either a series or a multiple wiring system may be used. In some _cases, isolating transformers are used with the lighting fixture on a series system. On new projects, either overhead or underground distribution may be used. In recent years, underground distribution has become more popular. This is especially true where hollow steel or aluminum standards or poles are to be used. Ballasts and/or isolating transformers can be mounted in the bases of the standards, making access to these units easier for inspection and replacement. Only the size of wire required to feed the lamps on that particular standard must be carried up the pole to the fixture. This smaller wire size makes fixture connections easier. Underground distribution offers more protection to the distribution cables than do overhead systems.

CAUTION: Mercury-vapor and metal halide lamps are highly efficient, energy-saving lamps, but if broken they may give off dangerous ultraviolet radiation. A number of publications have been published warning of this danger. If you find yourself in the position of having to work with or around these high-discharge lamps, it is advisable to become aware of the information contained in the Occupational Safety and Health Administration (OSHA) standards, NAVSEA-INST 5100.3B, and NAVELEXINST 5100.7.

As mentioned, high-intensity mercury vapor and halide lamps can be dangerous if they continue to operate when the outer globe of the bulb is broken, punctured, or missing. A broken outer globe allows the lamp to emit intense ultraviolet radiation. PERSONS EXPOSED TO EXCESSIVE AMOUNTS OF ULTRAVIOLET RADIATION CAN SUFFER SEVERE SKIN BURNS, PAINFUL AND EVEN PERMANENT EYE DAMAGE, AND, IF THE EXPOSURE IS INTENSE OR REPEATED, PERHAPS EVEN SKIN CANCER.

If plans require the installation of mercuryvapor or metal halide lighting in an area ordinarily occupied, care must be taken to prevent injuries by following these simple instructions:

Use bulbs that have extinguishing devices.

Use totally enclosed lighting fixtures with protective shields that protect the lamp from damage and absorb ultraviolet radiation.

As a special warning for underground series circuits using HID equipment, the system will require auxiliary equipment to provide protection from high voltages caused by resonant power conditions that occur during "hot restarts." Failure to incorporate this equipment will cause lamps to blow, sockets to flash, or ballasts to fail. The individual manufacturer of the particular equipment to be installed should be consulted as to what hot start preventer they provide or recommend.