This is a resistive sensor whose conductivity varies depending on the intensity of light received on its photosensitive part. The measurable spectral range (400 nm – 700 nm) coincides with the human visible spectrum so it can be used to detect light/darkness in the same way that a human eye would detect it.
Sensor specifications (LDR)
Resistance in darkness: 20 MΩ
Resistance in light (10lux): 5 ~ 20 kΩ
Spectral range: 400 ~ 700 nm
Operating temperature: -30 ºC ~ +75 ºC