Eternal light

Did you know that the longest lasting light bulb is more than 110 years old and it is still switched on? The Centennial Light is hanging from the ceiling of the Livermore-Pleasanton Fire Department at 4550 East Avenue, Livermore, California. It is a four-watt, hand-blown, carbon-filament, common light bulb manufactured in Shelby, Ohio, by the Shelby Electric Company in the late 1890s. The bulb was donated to the Fire Department by Dennis Bernal, the owner of the Livermore Power and Water Company in 1901, when he sold the firm.

The Centennial Light was switched off only a very few times which, despite the common belief, is the reason for its longevity. Each time a bulb is swithced on and off, the filament is heated and cooled down which makes the filament to expand and contract. These expansions and contractions create microscopical stress fractures in the material of the filament, which eventually lead to a break causing the bulb to burn out.

The last time was 33 years ago when the Centennial Light was switched off during the move of the Fire Department to its current location. The bulb spent 22 minutes without electricity while it was transferred.