The airplane was on final approach to land after the completion of a local night instructional flight. The flight instructor was to demonstrate the proper pitch attitude and sight picture needed for a landing at night. On short final, just before touchdown, the airplane drifted off of the runway center line to the left. Upon touchdown the airplane was still moving toward the left side of the runway. The instructor pilot stated that with the low energy state of the airplane there was not enough room to perform a go around safely. The airplane then exited the runway as flight control inputs were applied to correct back to centerline. Upon exiting the runway, the airplane impacted a runway light on the lower portion of the right wing strut attach point, resulting in structural damage to the strut. The instructor pilot reported that the accident could have been prevented if positive control was maintained during the landing phase of the flight.