The light dependent resistor (LDR), or photo-resistor, is a variable resistor that depends on incident light (as opposed to the position of a shaft in a potentiometer).
The resistance decreases as light is increased. In the dark, resistances in the order of can be achieved. In very bright light, resistances are in the order of 100s of
.
![](https://blogs.plymouth.ac.uk/embedded-systems/wp-content/uploads/sites/94/2018/10/LDR-Symbols.png)
Used in a potential divider circuit, a simple light-to-voltage can be created.
![](https://blogs.plymouth.ac.uk/embedded-systems/wp-content/uploads/sites/94/2018/10/LDR-Circuit.png)
The resistance is also dependent on temperature, so these devices are not ideally suited to accurate measurement or instrumentation.