In this project, we will go over how to build a motion sensor light circuit with an arduino. A motion sensor light circuit is a circuit in which a light turns on when motion is detected. With a PIR motion sensor integrated with an arduino, we can detect movement and program the arduino to turn a light on for a certain period of time once this motion is detected. For example, once motion is detected, we will turn on the light attached to the output of the PIR sensor for 1 minute. This is how most commercial motion sensor lights work. When motion is detected, the light will turn on for about 1 or 2 minutes. If the light turned on and stayed on for only the second that motion is detected, this wouldn't be very useful. When motion is detected by a motion sensor light, it will stay on for at least a period of time, on average 2 minutes, so that it can provide light.