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Note: This document is a continuation of
Understanding Early Street Light Circuits
The development of single lamp circuits - installations that involved power supply, photocontrol and illumination of a single luminaire - was primarily influenced by the development of a practical photoelectric switch, also known as a photocontrol. Early photocontrols were bulky, expensive and not very reliable. While these devices were contemplated as early as the 1920s, photoconductive and photovoltaic components back in that day were pretty feeble and could not generate or pass very much current. As a result, tubes were required to amplify this current to a sufficient level so as to operate a relay. Early photocontrols could be affected by cloud cover and could trigger false turn-ons. Some devices would chatter, causing lights to flicker, or be affected by the lights themselves when they turned on. As a result the more reliable photocontrols were large and complex, and expensive. A snapshot of a few of many patents helps explain the evolution of the photocontrol and the resulting economy in operating single lamp circuits. Finally the cost of the photocontrol became less than the cost to set up series or multiple circuits. In 1941, American Gas Accumulator Co. approached the photocontrol problem by usng a U-shaped
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