This is a light-controlled LED light Dark sensor circuit, a Light-activated switch, which fully depends on Light. LDR is a Light Dependent Resistor, which resistance increases in darkness and its resistance is. Light Sensors are photoelectric devices that convert light energy (photons) whether visible or infra-red light into an electrical (electrons) signal What Are Light Sensors? A Light Sensor generates an output signal indicating the intensity of light by measuring the radiant energy that exists in a. A tutorial on How to make a Light Sensor / Darkness detector circuit on breadboard using LDR and a transistor. This circuit can be used to automatically control and turn on-off lights or any loads depending on the brightness of ambient light, by adding a relay at the output. In. To design a circuit that detects darkness using an LDR (Light Dependent Resistor). Its resistance changes based on light intensity.