Circuit concept The circuit senses the ambience of light and depending on the presence/absence of sufficient ambience light. it turns the bulb on/off automatically The bulb gets on when there is insufficient ambience, and switches off when enough ambience is present This circuit does its job automatically without manual operation
LDR Light dependent resistor A resistor that act upon light exposure. The circuit symbol is box with a circle. When light falls on the LDR, the resistance, hence the voltage coming across it is decreasing.
How it works During daytime, when light falls on LDR,the resistance of LDR decreases.the decrement of resistance causes more potential to the other resistor.the potential of across LDR is directly transmitted, because of the low potential difference, across base and emitter, one of them goes cutoff restricting any flow of current from collector to emitter, turning the lightbulb