This is a very small light sensor. A photocell changes (also called aphotodetector, photo resistor, CdS or photo conductive cell) resistance depending on the amount of light it is exposed to. These little sensors make great ambient light triggers (when light in the room turns on, do something)

Working Principle of LDR:

Alight dependent resistorworks on the principle of photo conductivity. Photo conductivity is an optical phenomenon in which the materials conductivity is increased when light is absorbed by the material. When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy strikes on the device, more and more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more currentstarts flowing through the device when the circuit is closed and hence it is said that the resisitance of the device has been decreased. This is the most commonworking principle of LDR.

Circuit Diagram:

Here the LDR and R1 form a simple ‘Potential Divider’ circuit. When the light level decreases, the resistance of the LDR increases. When the resistance increases w.r.t to the other resistor having fixed resistance, the voltage drop across LDR increases.

Specification:

• Maximum voltage: 150 V, DC
• Maximum power: 100 mW
• Working temperature: -30 ° C ~ 70 ° C
• Spectral for peak: 540nm
• Bright resistance (10lux) (kΩ): ​​20-30
• Dark resistance: 2 MΩ
• 100λ10: 0.6
• Response time: 20 ms (increase), 30 ms (below)
• Lighting resistance: 4
• Size 7mm

Features:

• Light resistance : ~1k Ohm
• Dark resistance : ~10k Ohm
• Max voltage : 150V
• Max power: 100mW* 2 x 4 x 5mm
• 4mm between pins
• 28mm lead length

Applications:

• Burglar Alarms
• Light Detectors
• Light Sensor
• Color Sensor
• Line Sensor
• OBJECT SENSOR
• Photo Switch
• Lighting Controls For Street Lamps
• Light Intensity Meters