| 摘要 |
Light-sensitive switch structure for and method of turning a street light, or other load, on or off in response to varying light levels. The switch is designed to recognize the daily variations in light level and is capable of switching a load off at a light level lower than that at which the load is switched on. In a preferred embodiment the switch consists of a photo-sensitive element, two relays with time delay features, and two current limiting resistors to regulate the current flowing through the operating coils of the relays. In other embodiments wherein the values of the circuit components are properly selected one of the resistors regulating the current flowing through the operating coils of the relays may be eliminated. In accordance with the method of the invention one of the relays operates contacts which energize or de-energize the load, while the other relay operates contacts which connect or disconnect the resistors to or from the operating coils of the relays. The resistors function in concert with the varying resistance of the photo-sensitive element to provide the desired operation of the relays to effect the desired energizing of the load with an inverse light level ratio.
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