Lighting the Way: Industrial & Municipal Lighting (M)


Metal-halide lamps are energy efficient and produce good color for television broadcasts. Here they illuminate Jacob's Field in Cleveland, Ohio, 1994. © General Electric Company

We are seeking information about changes in industrial and municipal lighting over the last few decades. The following overview represents our starting point.

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ENERGY-EFFICIENT lamps for factories, parking lots, stadiums, and highways have been around for several decades. Two major varieties -- low-pressure sodium and high-intensity discharge -- are more powerful than fluorescents, more efficient than incandescents, and appeared before the Energy Crisis of the 1970s.

The lamps have grown steadily more efficient over the years, but industrial and municipal lighting still consume roughly as much energy as forty years ago, about 16 percent and 3 percent respectively. The answer to this riddle lies in the tremendous growth of this kind of lighting -- every kilowatt saved by technical innovation has gone to power new streetlights or factory lamps or stadium arrays. In the last decade, the spread of outdoor installations has fueled a new controversy -- a growing number of people have come to see the United States as a place excessively well-lit.

Since their debut in Europe in 1932, low-pressure sodium (LPS) lamps have been the most energy-efficient lamps available. Developed cooperatively by the European manufacturers Philips, Osram, and GEC, they gave about 50 lumens per watt (today's versions give nearly 200 lpw). So the problem of creating an energy-efficient lamp for factories and towns might seem to have been solved more than sixty years ago. The light from LPS lamps, however, is stark yellow. In their glow, everything appears either yellow, black, or some shade of gray, although some studies indicate that contrasts are clearer in LPS light, making them very good for street lighting. Largely because of the color, LPS lamps have sold poorly in the United States, compared to Europe.

An alternative to LPS lamps appeared at almost the same time. Mercury-vapor lamps introduced in 1932 by England's GEC were easy to use and produced 40 lpw. While not quite as efficient as low-pressure sodium lamps, they quickly replaced older sources of large-area lighting: tungsten-filament and carbon-arc lamps. Many people find the blue-green color a bit garish, though. Researchers have tried for years to overcome this drawback, principally through the use of phosphors, with only modest success.

Dissatisfaction with the color of these lamps helped to drive innovation in both types in the 1950s and 1960s. Scientists at General Electric invented a new ceramic material called polycrystalline-alumina, or Lucalox, that allowed sodium lamps to operate at high pressure. This improved the color from yellow to "golden white," but reduced efficiency. Initially giving about 80 lpw, the most efficient high-pressure sodium (HPS) lamps now produce about 110 lpw. HPS lamps with even better color have been developed, but their output drops still lower to the 40 to 60 lpw range.

At about the same time, the effect of dosing mercury-vapor lamps with halide compounds of various metals was under study by several inventors in West Germany and at General Electric. The goals were to improve color, save energy, and preserve brightness. The resulting metal halide lamp, introduced by GE in 1962, produced a whiter light at nearly 100 lpw. This lamp became very popular with the entertainment industry in the 1960s with the spectacular growth of live color-television broadcasts, such as sporting events.

The new HPS and metal-halide lamps, known generically as high-intensity discharge (HID) lamps, were expensive in the 1960s and had assorted teething problems. Like fluorescent lamps, HID lamps required a ballast to control the current flowing through them, and neither of the new lamps worked especially well with existing mercury-vapor ballasts. The shape of existing reflectors and housings for the lamps could also create difficulties.

Ultimately, the best solution to these problems was to install ballasts and fixtures specifically designed for the new lamps. This forced customers to decide which type to buy, and either choice could be expensive. To made the decision even harder, mercury-vapor lamps lasted a long time -- installing a new HID system meant justifying the replacement of working equipment. Adding to the confusion, some companies sold the new HID lamps as direct replacements for mercury-vapor lamps, while other companies with different marketing strategies sold them as completely new systems. Most industrial and municipal buyers stayed with familiar and cheaper mercury-vapor lamps.

Continued refinement of HID lamps throughout the 1960s, including a redesign of HPS lamps in 1968, addressed many early technical problems. And within a few years, the cost of electricity started to rise. Until then, the major costs of a streetlight or factory lamp were purchase price and maintenance -- energy was cheap. The OPEC Oil Embargo in 1973 ratcheted up the price of electricity, changing the economics of lighting. Cities began dousing streetlights.

With the new more efficient HID lamps already available, factories and local governments just needed to find the money to pay for the new equipment. But rising inflation amid a sluggish economy -- the "stagflation" of the 1970s -- worked against them. Lighting was a low priority for many factory owners as plants closed and unemployment grew. New streetlights were a tough sell to taxpayers, despite the complaints when lights were turned off to save energy. Many industries and municipalities simply stuck with their existing systems until the equipment wore out and then installed energy-efficient technology.

Solid-state electronic ballasts have added only small efficiency gains in HID systems. A phenomena of physics called "acoustic resonance" makes running HID lamps on high-frequency difficult. Some lighting controls, such as photocells and timers, were already widely used for streetlights. Dimmers have been more problematic for HID lamps than for fluorescents, and occupancy sensors are tough to justify for lamps that usually take several minutes to reach full power.

Ironically, older low-pressure sodium technology has recently enjoyed a resurgence in the United States. Whether the energy savings outweigh the poor color remains a matter of debate in the lighting industry. The discussion took an environmental turn when astronomers (and others) recommended LPS as one way to combat the hazy glow that hangs in the urban night sky. The yellow LPS light seems to contribute less than white light to "light pollution" and is easier to filter out of astronomical observations. New "full cutoff" fixtures, and adapter hoods for older fixtures, have been introduced to direct more light toward the ground. So, as businesses and local governments think about installation costs, energy efficiency, and white vs. blue vs. yellow light, they also have a preservation issue to consider -- how to save the night sky?

We hope to document more of the recent history of energy-efficient lighting. You can help by responding to a few questions on one (or more) of the Collecting History pages on this site. If you have helped to make or distribute efficient industrial and municipal lighting, or if you have used these devices in your business or workplace, we invite you to give us the benefit of your experiences. Your responses will help us better understand both the history -- and the consequences -- of this technology.