The LDR 5mm sensor works best in both Light and dark regions. Light-dependent resistors or photoresistors are a staple of electronics. If you need a way to sense the level of ambient light then there is no easier way to do it. As the light on the sensor increases then the resistance across the two leads decreases.
Analog Applications:
1. Camera Exposure control
2. Auto slide focus ? dual cell
3. Photocopy machines ? the density of the toner
4. Colorimetric Test Equipment
5. Densitometer
6. Electronics scales ? dual cell
7. Automatic gain control ? modulated light source
8. Automated Rear View Mirror
Digital Applications:
1. Automatic Headlight Dimmer
2. Nightlight control
3. Oil burner flame out
4. Streetlight control
5. Absence / Presence (Beam breaker)
6. Position sensor