Light Dependent Resistor (LDR) Operated Transistor Switch

The light dependent resistor (LDR) forms the sensor device that detects light as it falls on the LDR. When the light falls on the LDR, the resistance of the light dependent variable resistor LDR is decreased. The decrease in resistance value at the base will lead to more current to flow towards the base. The base voltage gradually increases above 0.7 volts that transistor begins to conduct. The LED connected to the collector circuit of the transistor glows up.