Photocell Light Sensor (12mm)
The is a light sensor which is also referred to photo resistor. The resistance will change depending on the intensity of light it is exposed to. This light dependent resistor has a diameter of 12mm. The resistance is roughly 200ohm with light and 20Mohm when dark.
Interfacing Circuit for LDR
The output of LDR is resistance hence it cannot be connected directly to any ADC. So a voltage divider circuit has to be constructed. You can see a simple voltage divider circuit whose output voltage is proportional to the light intensity of the light falling on the LDR. This output voltage can then be given directly to an ADC to measure the light intensity or to a comparator circuit.
Vout= Vin x (R1/(R1+RLDR))
Vout = Output Voltage of Voltage Divider Section
Vin = Input Voltage of Voltage Divider Section in our condition its 5 Volts
RLDR= Resistance of LDR