On September 8, 1999, at about 1437 eastern daylight time, a Piper PA-24-250, N980AC, registered and operated by Naples Air Center, operating as a 14 CFR Part 91 personal flight, experienced a collapse of the landing gear on landing rollout at Naples Municipal Airport, Naples, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was initially reported to have sustained minor damage, and was upgraded to substantial damage on September 23, 1999. The commercial pilot, and pilot-rated passenger reported no injuries. The flight originated from Marathon, Florida, about 47 minutes before the accident. The pilot stated she completed the prelanding check and lowered the landing gear about 5 miles from the airport. She did not see a green light and recycled the landing gear with negative results. She recycled the landing gear two more times with negative results. She contacted Naples tower and asked if they could see the landing gear. She was informed that a medical evacuation aircraft was close by. The medical evacuation pilot informed her that the landing gear appeared to be down. The tower also informed her that the landing gear appeared to be down on short final. A manual gear extension was not attempted based on the medical evacuation pilot and tower reports, even though she had an unsafe landing gear condition. The pilot thought she had a bad light bulb. She only had 1 hour in the airplane and was not that familiar with it. The approach was continued to a smooth touchdown. The landing gear collapsed on landing rollout, and the airplane came to a complete stop. Examination of the airplane by the FAA and recovery personnel on the runway, revealed the master switch, strobe, and navigation lights were on. The chief inspector for Naples Air Center Inc., stated, "When navigation lights selected to on position the landing gear indication lights are automatically dimmed for night operation. This is a normal condition." The FAA inspector stated, when the navigation light switch was turned off, the down landing gear indicator light went to the full bright position. The airplane was raised by maintenance personnel and jacks were installed under the airplane. The landing gear was successfully extended manually in accordance with the manual gear extension procedures. The master switch was selected to the on position and the green "down and locked" indication light illuminated. The airplane was towed to the maintenance hangar for further analysis. The airplane was placed back on jacks and the landing gear was raised. A functional check of the landing gear horn and all landing gear indication lights was performed with negative results. The flight instructor stated the pilot received a 1.2-hour check out in the PA-24-250. He was not aware of any previous landing gear problems with the airplane. He also confirmed that the landing gear down indicator light was hard to see.