Willis Lamm's
Traffic Signal Collection

(And Street Lights Too)

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  Line Material (L-M)
Dished Radial Wave
Series Street Light

Most early street light systems involved "series" circuits. A large number of street lights were supplied in series by high voltage. A regulator stabilized the voltage and the circuit used a single wire that made a loop out through each light in the circuit and came back to the regulator. In the days before photoelectric controls, a single switch or clock could turn on literally dozens of lights at one time. The high voltage series circuit also provided more light output per watt of energy consumed.

The first series systems used isolation transformers at each light to keep the whole string from going dark if a bulb failed. Later, the "film cutout" was invented. If a bulb failed the circuit's potential at the failed light would go extremely high, melting the cutout's insulating film and restoring the circuit. The process happened so quickly that the other lights on the string never went dark.

This particular light is called a radial wave, based on the shape of the reflector. Other reflector designs were also used, as well as luminaires that had glass refractors (globes.)

The parts shown include a ceramic luminaire, the mounting hub, the bulb socket and the radial wave reflector. This particular reflector is a "dome" type that would normally be used with 2500 lumen lamps. (GE was the first to introduce the dome reflector in 1917.)

The light disassembled.

In these early lights porcelain was used to insulate the high voltage potential in the lamp's wiring. Separate wires were attached to each side of the luminaire and the lamp socket plugged in between the spring loaded jaws. If the socket was not inserted, the jaws kept the circuit closed so that the series string would stay lit.

Four screws in the mounting hub hold the luminaire onto the hub, and four clamps hold the reflector onto the luminaire.

The luminaire "head."

The socket blades normally clasp the film disc cutout. When the lamp is used on 110 volts in a restoration, these blades must be kept separated by a thin piece of insulating material or they will create a direct short circuit. With this lamp I used a thin strip of Bakelite shaped to fit between the blades.

When inserting the socket it is important that the blades be inserted entirely into the luminaire or the bulb and socket can fall out.

The series socket.

The reassembled lamp is ready to be mounted. I used 6 gauge wire to reproduce the look of the old series wiring, however any wiring of proper size for the lamp load and environmental conditions would be suitable.

If you restore an old series street light and plan to light it, please remember that by its design it will create a short circuit if the lamp socket is not plugged in and the socket blades are separated by some suitable insulation material. The old porcelain fixtures have external lugs and strain reliefs for the supply wiring and those are "live" when the light is powered up. So mount series lights in a safe place away from children or pets that could touch live components.


In service as part of the collection.
Provenance. This light originally hung over the intersection of Clark Ave. and Freed Ave. in Pittsburg, CA, in an area that was originally Camp Stoneman, an Army camp. It had been overlooked when the series system was removed and eventually its conductors had separated from the pole insulators and were hanging in the intersection. I advised a friend who worked for PG&E of the problem and he corrected it. A few weeks later I found the street light sitting in my driveway.

These old luminaires can also be used outdoors to provide interesting area lighting. We used them around the ranch for night lighting.

Screw-in socket adapters can be used in order to light conventional house bulbs and some compact fluorescent bulbs have larger outside globes and look pretty nice in the old series lights, while still providing low cost lighting. These old fixtures are definitely worth saving and restoring.

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GE "Admiral's Hat" Street Light

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