This is an example of an "alphabet" bulb made by G.E.C. and sold under the "Osglim" in England. Similar glow lamps were made by American General Electric and the Birdseye Electric Co. Such glow lamps contain a single letter or number inside that glows when energized. These lamps could be arranged in a socket array to form words or addresses, well suited for advertising purposes. These lamps were made in both "base up" and "base down" versions.