THE NERNST LAMP
Dr. Walther Nernst, of Germany, investigating the rare earths used in the Welsbach mantle, developed an electric lamp having a burner, or “glower” as it was called, consisting of a mixture of these oxides. The main ingredient was zirconia, and the glower operated in the open air. It is a non-conductor when cold, so had to be heated before current would flow through it. This was accomplished by an electric heating coil, made of platinum wire, located just above the glower. As the glower became heated and current flowed through it, the heater was automatically disconnected by an electro-magnet cut-out.
Nernst Lamp, 1900.
The burners consisted mainly of zirconium oxide which had to be heated before current could go through them.
The resistance of the glower decreases with increase in current, so a steadying resistance was put in series with it. This consisted of an iron wire mounted in a bulb filled with hydrogen gas and was called a “ballast.” Iron has the property of increasing in resistance with increase in current flowing through it, this increase being very marked between certain temperatures at which the ballast was operated. The lamp was put on the American market in 1900 for use on 220-volt alternating current circuits. The glower consumed 0.4 ampere. One, two, three, four and six glower lamps were made, consuming 88, 196, 274, 392 and 528 watts respectively. As most of the light is thrown downward, their light output was generally given in mean lower hemispherical candlepower. The multiple glower lamps were more efficient than the single glower, owing to the heat radiated from one glower to another. Their efficiencies, depending on the size, were from about 3½ to 5 lumens per watt, and their average candlepower throughout life was about 80 per cent of initial. The lamp disappeared from the market about 1912.