Handmade Berry's Patents Magic Coal Fire bulb. This English lamp was used in "electric fires" or what Americans would call electric heaters. These bulbs were used to give a fire effect inside of an electric heater but a need arose to develop a bulb with a "rough service" filament since filament breakage was common in early electric fires due to vibrations from movement, the blower motor, etc. Such rough service bulbs were put into use which this bulb is an example of. They were fitted with a special two prong base meaning that whenever a bulb burned out a new one would have to be purchased from Berry, and the price was more expensive. This bulb dates to around the late 1940s.