Centennial Light, Incandescent light bulb in Livermore, United States.

The Centennial Light is a hand-blown incandescent bulb with a carbon filament, hanging from a black cylindrical socket with a small switch lever on its right side. Its amber-orange glass globe narrows to a neck at the top, and inside a tangled filament loop and spiral coil give off a dim orange glow. It hangs at Fire Station 6, 4550 East Avenue, Livermore, California.

The Shelby Electric Company of Shelby, Ohio, made the hand-blown carbon-filament bulb in the late 1890s; Dennis Bernal, owner of the Livermore Power and Water Company, donated it to the Livermore fire department in 1901. It hung first in a hose cart house on L Street, later in a downtown garage, and moved to Fire Station #6 at 4550 East Avenue in 1976, off for 22 minutes. Reporter Mike Dunstan brought it Guinness recognition in 1972.

Firefighters never turn off the bulb and treat it as part of their daily routine on duty. Visitors can follow its faint glow from home through a webcam at any time.

The firehouse sits on a main road and is easy to find when driving into town. You can look through the window or step inside during open hours when firefighters are present.

The bulb has been turned off only a few times, mostly for relocations or building renovations. Scientists believe the rare shutdowns and steady operation might explain its longevity.