Compact circuit, Can be wired in parallel to existing switches
This device allows one or more lamps to illuminate at sunset and turn off at dawn.Q1 and Q2 form a trigger device for the SCR, providing short pulses at 100Hz frequency. Pulse duration is set by R2 and C1.When the light hits R1, the photo resistor assumes a very low resistance value, almost shorting C1 and preventing circuit operation. When R1 is in the dark, its resistance value becomes very high thus enabling circuit operation

Circuit Diagram: Activated 220 volt AC Lamp Circuit Diagram



R1 = LDR
R2 = 100K
R3 = 200K
R4 = 470R
R5 = 12K
R6 = 1K
R7 = 470R
C1 = 10nF-63V
D1 = TIC106D
D2 = 1N4007
D3 = 1N4007
D4 = 1N4007
D5 = 1N4007
Q1 = BD327
Q2 = BD337
SK1 = Female Mains Socket


  • R3 allows fine setting of operating threshold and R2 value can be raised to 150K maximum.
  • Several lamps wired in parallel can be connected to the circuit, provided total power dissipation of the load does not exceed about 300 - 500W.
  • PL1 can be omitted and the input mains supply wires connected in parallel to any switch controlling lamps. In this case, if the switch is left open, the circuit will be able to drive the lamps; if the switch is closed, the lamps will illuminate and the circuit will be by-passed.
  • Warning! The circuit is connected to 230Vac mains, and then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.