LDR Sensor

LDR sensor (Light Dependent Resistor) is a device which is used to detect light. It has a (variable) resistance that changes with the light intensity that falls upon it.This allows them to be used in light sensing circuits.They are used in many consumer products to determine the intensity of light.

An LDR or light dependent resistor is also known as photo resistor, photocell, photoconductor. It is a one type of resistor whose resistance varies depending on the amount of light falling on its surface. When the light falls on the resistor, then the resistance changes. These resistors are often used in many circuits where it is required to sense the presence of light. These resistors have a variety of functions and resistance.

For instance, when the LDR is in darkness, then it can be used to turn ON a light or to turn OFF a light when it is in the light.A typical light dependent resistor has a resistance in the darkness of 1MOhm, and in the brightness a resistance of a couple of KOhm.

ldr sensor


Max power dissipation 200mW
Max voltage @ 0 lux 200V
Peak wavelength 600nm
Min. resistance @ 10lux 1.8kΩ
Max. resistance @ 10lux 4.5kΩ
Typ. resistance @ 100lux 0.7kΩ
Dark resistance after 1 sec 0.03MΩ
Dark resistance after 5 sec 0.25MΩ


The bigger one wire is +ve of LDR  and other is -ve.

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