A bulb that may have been burning since the early 1900s has been discovered glowing dimly in the basement of the Fire Museum of York County, Pennsylvania.
Dennis Kunkle, director of facilities for the York County History Center, sent pictures and a description of the old bulb to an antique radio forum, which told him about the origin of the dual filament bulb.
The Phelps HYLO, "HIGH-LOW" bulb, patented in 1904, was designed to save electricity.
According to a period advertisement: "One cent will buy electricity enough to run a HYLO turned down for 12 hours ... It is a lamp which will give you either a 16 candle power light or a 1 candle power light, without any waste of current by simply turning down as easily as turning down a gas jet." This is in reference to gas lighting, popular around 1900.
Observing the bulb in operation, low is indeed equal to the light of one candle.
A flexible contact on the base of the bulb allows the second filament to be turned on by screwing it in a little tighter.
Kunkle can't say for certain how long the bulb has been operating in the basement of the fire museum, but since the building was built in 1903, it is possible that the bulb has been with the building since the beginning.
Kunkle went on to say that the smoky coating inside the bulb indicates that it probably contains carbon filaments. Carbon filaments were replaced with tungsten in light bulbs after about 1920
The bulb was removed from the basement socket of the fire museum this week and added to the York County History Center collection.