● This circuit is based on Light Dependent Resistor (LDR) which will turn on LED's when ever darkness is sensed in room. You can put this small lamp in your child's room as a simple emergency lamp to avoid panic situation in case of sudden power failure. As it provide ample of light in the room so that your child can easily come out of room.
● Important feature of this LDR based automatic lamp circuit is it automatically become on by sensing the darkness so no need to search for switch.
● And it is powered by a rechargeable battery which charges automatically by the AC power supply so no need to worry about the battery backup.
● You can use adapter readily available in market or make your own power supply with the help of transformer and bridge rectifier.
● And when light comes it automatically off the lamp so need to off the lamp manually.
Fig. 1: Prototype of LDR based Automatic Lamp Circuit on Breadboard
This circuit explains the principle of operation of LDR (light dependence resistor). LDR is a device whose sensitivity depends upon the intensity of light falling on it. The resistance of LDR decreases when intensity of light falling on it increases and vice versa (resistance increases when intensity of light falling on it decreases). In dark or in absence of light, LDR exhibits a resistance in the range of mega ohms, which decreases to a few hundred ohms in presence of bright light.