LIGHT OPERATED

SWITCH

Dinieta Indiarni

Ines Adhiaksono Putri

Circuit

LDR

battery

Rb

Ra

Light bulb

Circuit concept

The circuit senses the ambience of light and The circuit senses the ambience of light and depending on the presence/absence of depending on the presence/absence of sufficient ambience light. it turns the bulb sufficient ambience light. it turns the bulb on/off automatically The bulb gets on when on/off automatically The bulb gets on when there is insufficient ambience, and switches there is insufficient ambience, and switches off when enough ambience is presentoff when enough ambience is present

This circuit does its job automatically without This circuit does its job automatically without manual operationmanual operation

LDR

Light dependent resistor Light dependent resistor

A resistor that act upon light exposure. The A resistor that act upon light exposure. The circuit symbol is box with a circle . When light circuit symbol is box with a circle . When light falls on the LDR, the resistance, hence the falls on the LDR, the resistance, hence the voltage coming across it is decreasing.voltage coming across it is decreasing.

How it works

During daytime, when light falls on LDR,the During daytime, when light falls on LDR,the resistance of LDR decreases.the decrement of resistance of LDR decreases.the decrement of resistance causes more potential to the other resistance causes more potential to the other resistor .the potential of across LDR is directly resistor .the potential of across LDR is directly transmitted , because of the low potential transmitted , because of the low potential difference, across base and emitter, one of difference, across base and emitter, one of them goes cutoff restricting any flow of them goes cutoff restricting any flow of current from collector to emitter, turning the current from collector to emitter, turning the lightbulblightbulb