At the time, I was doing some contract flying in the right seat of a Piper Cheyenne twin turboprop. My first flight was at night, departing from a busy Class B airport, and as we were cleared for takeoff, I called out the checklist items. Crossing the hold short line, I turned on the landing light just as I had done hundreds of times before in other airplanes in preparation for takeoff. The captain immediately smacked my hand on the switch, turned the light back off, and asked, “What are you doing?” I was obviously caught off guard. What I had failed to notice was the Delta 757 sitting across the runway on the opposing taxiway, which I had momentarily blinded with our landing lights.