littleBits Electronics Light Sensor
The light sensor measures how much light is shining on it. It has two modes: "light" and "dark." In "light" mode, the more light shines on the sensor, the higher the signal it sends out. In "dark" mode, it's just the opposite – the signal increases the darker it gets. You can use a screwdriver to adjust the sensitivity. Use a bargraph to see how it's working.