Photoresistor (LDR)

Picked up a five-pack for my Arduino weather station and the resistance shift from bright sun to room light is very clear. These are exactly what I needed for a simple dusk-to-dawn trigger circuit.

Just wired this into a garden light project and it's responding perfectly to changing sunlight levels. The resistance shift is very noticeable when I hold a hand over it.

Used one in a dusk-triggered LED circuit and the resistance shift was immediate when light hit it. Even in dim room light, the change was obvious enough to flip my transistor without any fiddling. Great little sensor for the price.