Willis Lamm's Traffic Signal Collection
(and street lights, too)
Information Sheet


In the late 1800s with the advent of electrical power systems, cities turned from gas to electrical street lighting. Electrical lamps could provide more illumination and they could be placed more prominently overhead. While gas lamps had to be lit individually each night or be left to burn all day, electric lights could be grouped together and controlled from one point.

In the 1800s there weren't photo controls so strings of lights had to be turned on manually or by time switches. Standard voltage electricity did not travel long distances without suffering line losses, so multiple lamp systems required that the lamps be located within a close area. To expand the distance that a circuit could be run - all around town rather than be limited to a couple of blocks - high voltage series lighting circuits were designed. These circuits typically ran at high voltage, with the lamps arranged in a series.

Series lamp circuits presented a few technical problems. Since current passed through all the lamps in series, when a lamp failed the circuit would open and the whole string would go dark. This problem was initially solved by installing auto transformers at each luminaire. The lamps were powered by the auto transformers and if a lamp failed, current lighting the string would continue to flow through the transformer so that the other lamps remained lit.

View early street light designs in a new window.

Another concern involved regulating the voltage. In a multiple (parallel) circuit the voltage stays the same but the amount of current needed increases as more lamps are added. In a series circuit there is a voltage drop across each lamp and the total amount of voltage needed to light the string depends on the number of lamps in the string. A constant current transformer, or regulator, had to be employed to adjust the circuit voltage as lamps burned out and were replaced.

Early carbon filament lamps had relatively low light output. As a result they were primarily relegated to area lighting or were used in groups of lamps, and carbon arc lamps were used for primary street lighting. With the invention of the tungsten filament Mazda lamp, incandescent lamps could give off large amounts of light. At that point the harsh, maintenance intensive carbon arc lamps gave way to more pleasant Mazda lighting.

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