AUTOMATIC EVENING LIGHT With Cut-Off Timer

Designing a circuit to switch on a light at dusk and off at dawn is straightforward, and many such designs have been featured in EFY.

- PRADEEP VASUDEVA

However, lights controlled this way remain on all night, resulting in wasted electricity and reduced lamp lifespan. In most homes and business premises, outdoor lights are turned on at dusk and switched off after a few hours. The device described here automates this process, activating the light in the evening and switching it off after 2 to 6 hours. This approach is particularly effective for securing locked homes, as the timed lighting creates the illusion of occupancy and deters potential intruders.

Circuit and working

Fig. 2 shows the circuit diagram of the automatic evening light. It is built around the dual op-amp IC LM358. The first op-amp, built around IC1A, is used as a comparator. The inverting pin 2 of the comparator is biased at half the supply voltage by resistors R1 and R2. During the daytime, the resistance of the LDR connected to the non-inverting pin 3 of the comparator is low. The voltage at the non-inverting pin 3 is lower than the voltage at the inverting pin 2, so the output at pin 1 of the comparator is low.

In the evening, the resistance of the LDR increases and becomes more than the resistance of R3 plus VR1, and the output at pin 1 of the comparator becomes high (that is, about 1.5 volts below the supply voltage). Potentiometer VR1 serves as sensitivity control.