20mm LDR Sensor Light Dependent Resistor Sensor also called photoresistor or LDR 20mm – Light Dependent Resistor is a resistor whose resistance decreases with increasing incident light intensity; in other words, it exhibits

Photoconductivity.

A photo-resistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. LDR(Light Dependent Resistor) also known as photoresistor is a resistor whose resistance varies with the amount of light falling on it. This is a small size LDR with a size of 4mm.

To use, connect one side of the photocell (either one, it's symmetric) to power (for example 5V) and the other side to your microcontroller’s analog input pin. Then connect a 10K pull-down resistor from that analog pin to ground. The voltage on the pin will be 2.5V or higher when it's light out and near the ground when its dark. This sensor can be used for making a light sensor, color sensor, object sensor, line sensor, etc.

Features of LDR 20mm – Light Dependent Resistor

1. Miniature open frame package.
2. Epoxy coated.
3. Moisture resistant.
4. Spectral response is similar to the human eye.

Applications of LDR 20mm – Light Dependent Resistor

1. Camera Exposure Control.
2. Auto Slide Focus – dual cell.
3. Photocopy Machines – density of toner.
4. Colorimetric Test Equipment.
5. Densitometer.
6. Electronic Scales – dual cell.
7. Automatic Gain Control modulated light source.
8. Automated Rear View Mirror.
9. Automatic Headlight Dimmer.
10. Night Light Control.
11. Oil Burner Flame Out.
12. Street Light Control.
13. Absence / Presence (beam breaker).
14. Position Sensor.