These lamps differ significantly from the traditional street series type because they operate directly from the voltage supplied by utility secondary distribution circuits (typically 120 volts) instead of the low voltage/ high amperage characteristics of street series lamps.

Multiple lamps have been utilized in street lighting installations ever since incandescent street and roadway lighting was introduced in the 1880s. Although relatively uncommon for street lighting applications until after World War II, multiple incandescents started to gain significant popularity versus the series type in the late 1940s. This trend continued through the mid to late 1960s. Individual and strings of multiple lamps could be operated from photoelectric lighting controls, which were declining in cost during the 1950s and 1960s. The convenience of multiple street lighting had gained much acceptance particularly on account of their safe operating voltage and lower voltage luminarie requirements. Municipalities and electric utilities realized the advantages of multiple operation street lighting and during the 1960s the trend pretty much across the United States was to retire aging, sometimes unsafe and less reliable series street lighting systems with simple, multiple operation luminaries, commonly incandescent of equal light output.

Through the 1910's series incandescent operation was the most popular method of streetlighting although multiple streetlights were occasionally used. During the 1930s multiple streetlighting became somewhat more popular although series operation was the general rule. When photoelectric lighting controls became more affordable in the late 1940s multiple streetlighting greatly increased in popularity. Utilities began to favor multiple operation streetlights because they operated at much safer voltages (typically 120V obtained from nearby secondary distribution circuits) than their series counterparts and were much less of a maintenance problem. Multiple fixtures without individual photoelectric controls were usually operated by a separate control on the pole or crossarm. Some of these multiple streetlights were operated in groups from one photocontrol that is capable of handling the higher amount of current required. During the 1950s streetlighting fixtures with integral photocontrols gradually became more popular than group-operated lights. In later years these fixtures became gradually less expensive, as well as their twist-lock photocontrols, therefore becoming increasingly more common with utility streetlighting systems, hastening the replacement or conversion of many aging series streetlighting systems starting in the 1960s.

Like their series counterparts, the multiple-operation lamps also were rated in terms of light output instead of wattage. For instance, a standard 3000-hour, 2500-lumen, 120-volt street lamp consumed 189 watts and a 4000-lumen one consumed 295 watts. Therefore "odd" wattages were associated with multiple streetlighting lamps. Extended service lamps required a small percentage of additional watts to produce the equivalent amount of light. For instance, a 2500 lumen multiple lamp rated at 6000 hours average life consumed an additional 13 watts (202 watts total). Although more energy was required by extended service lamps, utilities determined where the trade-off was by comparing reduced re-lamping expenses and the additional amount of energy required to operate the lamp through its rated life. Typically 3000-hour lamps were standard practice. Most incandescents were designed for group replacement service. That meant that the lamps were designed to be replaced all at once if they were operated in groups (series or multiple) from one control. Usually group replacement of lamps took place at a given percentage of rated lamp life (typically around 75%) so that a low percentage of burnouts would have already occurred at the time of group replacing. The primary advantage of this method of re-lamping was reduced labor costs compared to one-at-a-time lamp renewals.

Multiple streetlighting lamps rated at 3000 average hours life ranged from 600 lumens (58 watts) through 15,000 lumens (860 watts) - see below for list of ratings. All had clear outer bulbs and those 2500 lumens and less had medium (household size) screw bases. Mogul bases were larger and were available as an option for 2500 lumen lamps by some manufacturers and this screw base was standard for all multiple streetlighting lamps rated 4000 lumens and above. Outer bulb sizes were designed in accordance to lamp wattage; the higher the wattage (and light output) the larger the bulb. For instance, 58, 92, 189, 295, 405, and 860-watt group replacement service lamps typically had outer bulbs sized A-21, A-23, A-25, PS-35, PS-40 and PS-52, respectively. The alphabetic nomenclature employed described their basic outside shape or design and the following number represented the number in eighths of inches the lamp had at its widest point in diameter. Multiple streetlighting lamps are still being manufactured as of 1998, however the assortment and offerings of their wattages and light outputs has dwindled to generally the most commonly ordered sizes.

Like series lamps, multiple incandescent lamps are rated in light output, such as 1000, 2500, 4000 lumens, etc. In order to achieve these specific light outputs, odd wattages are attained, i.e., 92, 189 and 295 watts, respectively for 3000-hour group replacement lamps. Multiple incandescent street lamps differ from ordinary lamps in that they are designed to have their average lumens throughout life correspond approximately to the street series lamps of the same initial rating that they were replacing; thus, the odd wattages for most. The 1500-hour types have been utilized for one-at-a-time replacement while 3000-hour lamps and 6000-hour lamps were for biannual and annual group replacement, respectively. Some utilities have employed group replacement using these lamps while many others did not. Extended life lamps, containing krypton as a filling gas, are rated at 10,000 hours and 12,000 hours. It should be noted that in these instances lamp efficacy is sacrificed for longer lamp life. For instance the 1000 lumen, 1500-hour lamp is rated at only 85 watts while the same lamp designed for 12,000 hour operation consumes 105 watts. Multiple street lighting lamps are still being offered by most of the larger lamp manufacturers as of 1998. However they are available in the most commonly utilized lumen ratings and are designed for longer life, typically 6000 to 12,000 hours.

Through the years various lumen ratings with different and interesting wattages were offered. Many of the following were available through the late 1970s: The 1500-hour lamp was manufactured in the following nominal lumen / wattage ratings: 1000 (85W), 2500 (175W), 4000 (268W), 6000 (270W), and 10,000 (575W). The 3,000 hour lamps had a broader range and their lumen and wattage ratings were: 600 (58W), 800 (76W), 1000 (92W), 1500 (115W), 2500 (189W), 4000 (295W), 6000 (405W), 10,000 (620W), and 15,000 (860W). The 6000-hour lamps respectively were: 1000 (103W), 2500 (202W), 4000 (327W), 6000 (448W), and 10,000 (690W).

None of the above were krypton-filled lamps. These did not become available until the later 1970s for street lighting applications, and krypton has been typically used only in the extended service lamps, particularly the 1,000 and 2,500-lumen variety.

Multiple street lighting lamps at and below 2500 lumens were usually manufactured with medium screw bases; a few of the 2500 lumen ones and all others above this rating have mogul screw threads. Most could be operated in any burning position and all are of the familiar "A" (Arbitrary) or "PS" (Pear Shaped) outer bulbs. All were clear glass except for a very few that at least Sylvania made of what they called "Natural Blue" glass. These were available during the 1950s and 1960s (and possibly earlier) and were intended for identifying the location of police and fire emergency boxes mounted on the same utility pole as the luminarie. These special transparent blue lamps were uncommon and their intrinsic blue brilliance stood out at a considerable distance. They were available in the 58-watt (A-19 bulb) and 115-watt (A-23 bulb) sizes.

Other special multiple operation incandescent lamps available to users were ones with outer envelopes made of hard, borosilicate (heat resistant) glass - one example the author knows of is a 340 watt, 3000-hour lamp with a light output of approximately 4000 lumens. Also Vibration Service lamps in the 92 and 189-watt sizes were made for locations where traffic vibration was severe. Although all multiple incandescent street lighting lamps were rugged and designed to adequately withstand traffic, luminarie, and transportation shocks to a significant extent, the aforementioned two varieties had substantially more durable filaments and enhanced filament supports.

Multiple Incandescent Lighting

These luminaries differed from the series operation ones mainly because of their lower voltage insulation requirements. Since the multiples required only 120 volts to operate, high voltage insulation that was needed within the series units was not a factor in the multiples' design. Otherwise, multiple streetlighting fixtures were pretty much identical to their series counterparts through the 1950's. The giveaway, however, was the fixture having an integral or remotely installed photocontrol.

Multiple incandescent fixtures were offered along with the series operation styles in manufacturers' and electrical distributors' catalogs since the earliest days of electrically operated streetlighting, although the series units were far more in demand than the multiples until after World War II.

The majority of multiple incandescent operation fixtures were manufactured with cast aluminum or sometimes steel heads and most were internally wired. Some of the prominent manufacturers and distributors of incandescent streetlighting equipment offered multiple incandescent fixtures with porcelain heads; however their additional expense did not make them commonplace. Most of these had fixed-position sockets within them instead of the removable series-type sockets. After World War II practically all the multiple operation incandescent luminaries were manufactured in cast aluminum. The familiar "can-shaped" or "NEMA" style ones typically had the pipe slip-fitter attachment affixed to the body of the luminarie by bolts or screws. Single-piece, cast aluminum units superseded such "two-piece" fixtures by the early to mid-1960s. This was the case also for internally ballasted mercury luminaries which often utilized the same type of aluminum fixture bodies from the early 1950's on.

Multiple incandescent streetlighting fixtures utilized the same reflectors and globes as the series units and most were interchangeable since their physical method of attachment to the fixture head usually did not differ, especially with NEMA style latch-on optical assemblies. Therefore it was sometimes common practice during series to multiple conversions to reuse the same reflector and attaching glassware if it was in good condition.

Most multiple incandescent luminaries employed a stationary, fixed or adjustable position lamp socket which required "up in the air" re-lamping. A few manufacturers, such as the Wheeler Reflector Company employed a plug-in style porcelain or Bakelite socket that mated with a receptacle within their cast aluminum fixtures. These sockets had two brass prongs spaced about two inches apart and mated with a porcelain receptacle with two wire terminals on it. The advantage of the plug-in sockets was that lamp replacement could be readily and quickly accomplished in the same way as series lamps, using a special lamp renewal pole that had a hinge and collar grasping attachment on its end. Once the pole reached the socket in an open incandescent fixture the repairman would pull on a rope that ran along the side of the pole, allowing the socket changer's end collar to grip the socket's bottom flange. The lamp's socket was removed by maintaining tension on the collar rope and pulling down on the lamp change-out pole, then it was lowered down to where the operator could handle the bulb and socket, and the procedure was reversed to reinstall the bulb. This method of lamp replacement saved time and the cumbersome effort otherwise required by having to use a ladder or bucket truck to replace a defective lamp.

Radial wave and other porcelain enameled reflectors used with multiple incandescent fixtures were produced until the early 1970's. For some years prior aluminum reflectors were available and after the demise of the porcelain enameled ones, stamped aluminum reflectors were the standard. Unfortunately after several years of service these units lost their refecting surface effectiveness significantly since their undersides commonly turned to a light grayish, somewhat rough, pitted surface that absorbed light instead of reflecting it. Usually, these latter-day reflectors clipped onto regular aluminum heads having the industry standard method of optical assembly attachment. Multiple incandescent fixtures were available through the 1980's (and may still be) and these were simple NEMA heads with only a socket within them wired to a photocontrol receptacle on the fixture's top; otherwise identical to the ones with mercury and HPS ballasts presently made.

Radial wave aluminum reflectors met their demise during the late 1970's or early 1980's. Optical assemblies attached to incandescent multiple luminaries since then are of the simple aluminum reflector/plastic refractor, identical to those used in yard lights. Of interest, porcelain enameled radial wave reflectors with the good, old-fashioned green on top and white enamel on their undersides were produced for a short period during 1993-1995 by PEMCO (Philadelphia Electrical Manufacturing Company), a firm that was famous for many years for their streetlighting luminaries of all types. These porcelain enameled steel reflectors were produced in the deep bowl design from the original castings, which had not been used since 1974 when PEMCO discontinued radial wave reflector manufacture. Their early 1990's reflectors were used with standard NEMA heads that had 35 or 50-watt HPS ballasts built into them, intended as a form of reproduction historic-appearing streetlighting with a modern light source. When PEMCO met financial difficulties in late 1995-1996 the real McCoy porcelain reflectors were no longer made and have not been since. Although the company is apparently now under new management, their reproduction radial wave HPS fixtures are offered with a plastic-like, bendable and apparently weatherproof deep bowled, clip-on reflector that is identical in appearance to it's predecessor porcelain-enameled steel unit.

Series to Multiple Streetlighting Fixture Adapters

During the series to multiple streetlighting conversions which took place in prior decades some utilities simply retrofitted existing series streetlighting luminaries that were still in good condition for multiple operation. This was accomplished in one of two ways. One way was by removing the series socket and utilizing an adapter having two wire terminals affixed to its porcelain socket and was attached to a solid cast aluminum ("dummy") prong which was inserted into the series head. The low voltage streetlighting wires were run to the fixture (sometimes reusing the original series fixture leads) and then they looped directly to the multiple receptacle with the wires disconnected from the series terminals in the head. A photocontrol was usually mounted on the pole or crossarm, or on the fixture bracket itself. Several of these installations are photographed in the Incandescent Streetlight Pages.

Another method of utilizing the same series fixture for multiple streetlight operation was by simply inserting a mogul-to-medium socket adapter into the existing series socket and rewiring the lead-in conductors at the crossarm so that the luminaries operated from secondary voltage service. Utilities that employed this simpler type of conversion had to make provisions to assure the "fail-safe" methods of assuring series circuit continuity were defeated (the socket and the mogul to medium adapter had to be secured against removal). Otherwise the fixture would obviously short-circuit because the receiving prongs in the series head would spring together and unscrewing the socket adapter would cause the socket's center tab to short to the mogul screw base shell. Typically, such fixtures converted in this manner had weatherproof fuses connected to them for safety. The series cutout wafers inserted between the two socket prongs were replaced by a rigid piece of insulation material, such as a small strip of plastic or Bakelite before the converted socket was reinserted into the luminarie during the retrofitting process. Utilities who "recycled" their fixtures in this manner sometimes also repainted the luminarie's mounting bracket and replaced the reflector with a new one, if one was needed.

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