An oil lamp is a simple vessel use to produce light continuously for a period of time from a fuel source. The use of oil lamps extends from prehistory to the present day. While a basic form of lighting prior to the era of widespread electric lighting, oil lamps today are popular for mood lighting, as an alternative to candles, or as an alternate source of emergency lighting when electricity is not available. Many oil lamps provide a small wheel that when turned, moves the wick up and down so that the user can adjust the light produced. Some lamps sold now are both the traditional farmer's lantern, made mostly of metal, with a glass chimney, and the old-fashioned hurricane lamps, made mostly of glass, with only the wick holder assembly made of metal.