Reading light levels with an LDR and Arduino
A light dependent resistor is a component that changes its electrical resistance according to how much light falls on it. Bright light makes it conduct easily, darkness makes it conduct poorly, and an Arduino can turn that difference into a number. It arrives in two forms. The raw component is a small disc with two legs, and it needs one extra resistor to work. The other form is a sensor module, a small board with the component already soldered on together with everything else the circuit needs, ready to connect to the Arduino with three or four jumper wires. Both versions do the same job and both show up in real projects. Automatic garden lights, night lights, display backlight dimming or simple daylight loggers all work on the same principle.