New successful design in our lab[mfn]Designed and tested by one of our student under the guidance of faculty[/mfn]. Smallest circuit of STREET LIGHT CONTROL. Try it. It works very nicely, smoothly and effectively. Very sensitive to detect morning and evening light changes.
Required Material
- 230V, AC, 100W lamp with holder
- BTA12 Triac
- Any type of Diac
- Small, medium or large LDR
- Variable resistor (Carbon or WW) 500k
- Polyester capacitor 3.3nF, 400V min[mfn]The operating voltage of this capacitor must be very high. Do not use ceramic type capacitor at this position in the circuit.[/mfn]
Practically Test Circuit
In above circuit, the capacitor of 3.3nF used in the circuit must have operating voltage above 400V. The VR of 500k in the circuit may be the general purpose carbon or wire wound pot.
Photos of working circuit
When it is evening the LDR senses dark outside and switches the street light on 
In the morning the street light becomes off 
Smallest Circuit 
Really small…!
Precautions
- Do not touch any part of the circuit when it is live.
- To adjust the sensitivity of the LDR use small insulated screw driver to rotate the preset.
- Always connect this circuit in series of any load running on 230V AC.
- Do not use this circuit on DC[mfn]This circuit is designed in our lab with 230V AC mains power supply. You can use the same circuit on 110V AC, 60Hz with just a signle modification of capacitor (C), change its value to 2.2nF.[/mfn] power supply.
Vidyasagar Academy 