Automatic Switching “ON” and “OFF” of the Street Lights by Using Sunlight using the Photo-Electric Control

Street lights can be made to turn ON automatically when night time comes. Similarity they will turn OFF automatically when day comes. This system can be done by electrical control which utilizes a photo electric control device illustrated in figure below (A). Figure below (B-B1) shows how simple schematic diagram of the photo electric control.

(A) Actual photo electric device.

Control operation

(B) Simple schematic diagram of a photo electric device.

At night time when sunlight does not strikes the photo electric control device, the resistance of the photo resistor PR inside the photo electric device is high, see figure above (B). The current I that will pass through the thermal device T will be low. This low current I will not sufficiently heat and make the thermal device T to expand. At this condition, the normally closed contact B which is coupled to the thermal device T will remain close to energize contactor C. with contactor C energized, contacts C (1-2,3-4,5-6) will remain close to energize (turn-On) the street lights.

(B1) Simple schematic diagram of a photo electric device.

At day time, when sunlight strikes the photo electric control device, the resistance of the PR is reduce. The current I that will pass through the thermal device I increase and cause the temperature of the thermal device I to rise up. With rise up temperature, the thermal device T will expand and push the normally closed contact B to open. With contact B open, the contactor C is de-energize. Contact C (1-2,3-4,5-6) will open to de energize (turn OFF) the street lights. 

(C) Control circuit of a photo electric device with street lights loads connected to 3-phase power source.

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