Some garage door units have a switch on the wall that not only opens the door, but turns the light on and off like a normal switch would do. Check to see that you did not bump this switch causing the light to stay on. Also check the wires from the wall switch to the unit to assure that they were not shorted out causing the light to stay on as well. What brand and model unit do you have? knowing this can help us offer additional advice if this does not work for you.
could be a bad relay that is stuck in the on position. bad circuit