On December 24, 2017, about 1740 mountain standard time, a Piper PA-28R-200 airplane, N550D, was substantially damaged during a runway excursion on takeoff from runway 28 (8,204 feet by 150 feet, asphalt) at the Riverton Regional Airport (RIW), Riverton, Wyoming. The pilot and four passengers were not injured. The airplane was registered to Oracle Aviation, LLC and operated by the pilot as a 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and the flight was not operated on a flight plan. The flight was originating at the time of the accident. The intended destination was the Stanford Field Airport (U12), St Anthony, Idaho.The pilot stated that he initially departed from Millard Airport (MLE), with planned fuel stops at Gordon Municipal Airport (GRN) and RIW. After refueling at RIW, the pilot recognized that the landing light was not working. He noted that it was working during the previous flight into RIW. The pilot recalled having good visibility with the runway lights, but he did not have good depth perception. As the airplane approached the intersection with the crossing runway during the takeoff roll, he thought that they were approaching the end of the runway. He rotated the airplane in an attempt to lift off, but the airplane had not gained enough airspeed to become airborne at that point. He decided to reject the takeoff and, as he reduced engine power, he lost directional control and the airplane departed the left side of the runway. The pilot stated that there were no issues with the airplane during the accident takeoff, other than the inoperative landing light. He noted that a functioning landing light and a better review of the airport diagram might have prevented the accident. A review of the available weight and balance data indicated that pilot's calculation was complete and correct, and that the airplane was loaded within limits during the accident takeoff. The airplane was equipped with four seats and seatbelts. The pilot stated that two children occupied one seat and were sharing a seatbelt at the time of the accident takeoff. Federal Aviation Administration regulations do not require a landing light for operations under Part 91 unless they are conducted for hire. However, any inoperative equipment must be deactivated and placarded according to the regulations.