LDR

Light Dependent Resistors

An LDR is a component that has a (variable) resistance that changes with the light intensity that falls upon it. This allows them to be used in light sensing circuits.

LDR circuit symbol

The most common type of LDR has a resistance that falls with an increase in the light intensity falling upon the device. The resistance of an LDR may typically have the following resistances: 5000Ω light to 20000000Ω in the dark.

A common cadmium sulphide (CdS) LDR is the G5516 with a Spectral Peak of 540 nm (green light 560THz)

cadmium selenide (CdSe) is useful for infared detection

G5516 LDR CdS

Pmax 90 mW

Spectral Peak 540 nm (green light 560THz)

Photo Resistance 5 ~ 10 (10Lx) (KΩ)

Dark Resistance 0.2 MΩ min

ResponseTime Rise 30 mS

ResponseTime Decay 40 mS

LDR responce times of 30/40ms are a lot slower than photo transistors so no good for data transfer but ideal for general daylight senseing.

G5516 LDR dimentions