The 2-Filament 3-Way Incandescent Lamp

Incandescent lamps that contained two filaments instead of one have been around for a long time. Shown to the left are three carbon filament lamps that could emit two different light levels. In addition, an article appeared in 1902 for a Tri-Light regulating key-socket and lamp (Section 15, Miscellaneous Lamp Topics). It was an early effort with carbon filament lamps to achieve more than one level from the lamp.

An effort to reduce street lighting costs during late night hours in Paris, France was pursued through the use of twin-filament, high-frequency, remote-controlled tungsten-filament gas-filled lamps. The most common lamps had 200- and 500-watt filaments in a 500-watt size bulb. Following that effort, engineers in the United States developed a similar lamp for commercial lighting. Westinghouse announced, in 1933, a lamp with two tungsten filaments where either or both could be used at the same time. Quoting from the General Electric Review3:

"The three-light lamp contains two filaments, each of which may be burned either singly or in combination with the other, thus providing three different levels of illumination from a single light bulb. At present, it is being made in two sizes; one containing 150- and 200-watt filaments; the other 200- and 300-watt filaments. The smaller-size combination employs a bulb of the same size as that used in the regular 300-watt Mazda lamp, and the larger-size combination utilizes the same-sized bulb as that of a regular 500-watt lamp.

"Each of these lamps is equipped with a mogul screw base which has an additional center contact in order to permit separate control of each filament. A special socket is necessary to accomodate this new base...

"It is expected that the new lamp will find its first application in the field of commercial lighting, particularly for small and medium-sized establishments which have definite peaks and low points in the volume of store traffic. During the slack period, these stores desire to have their lighting systems turned on as an indication that they are open for business, but the lighting requirements are not particularly exacting. For the active business periods the majority of these stores could effectively use considerably more illumination than they do at present.

"In the past, the general practice has consisted of a lighting installation that served merely as a happy medium between the high- and low-point requiremnets. With the new three-light lamps, it will be possible to use the lower-wattage alone for minimum requirements, the higher-wattage filament for average requirements, and the two together to supply a high level illumination for active shopping periods.

"There are two wiring methods which may be used in installing the new lamps: first, to run a third wire from the lighting unit to the wall switch, thereby controlling both filaments from the wall; second, to locate a canopy switch on the ceiling at each fixture."

Two lamps that were designed for residential lighting appeared in the literature in 19349. One was for Indirect lighting while the other was for Semi-direct portable floor lighting units. These are shown to the left.

"Both lamps have bulb diameters of 3 3/4 in. and are inside frosted . The 250-watt on the left with medium screw base is known as the Indirect-Lite Mazda lamp and measures 6 1/2 in. in overall length. The three-contact mogul-base on the right, which is known as the Indirect Three-Lite Mazda lamp , has two filaments (100-watt and 200-watt) which may be operated separately or simultaneously. It has an overall length of 6 3/4 in."

After articles regarding the three-lite lamp appeared in the technical journals in 1935 the subject matter nearly disappeared from the technical literature. To a large extent this was due to the emphasis in the late 1930s on fluorescent and mercury lamps. Then, in the early 1940s, restrictions were in effect on new lamp designs that were not aimed for the war effort. In a General Electric publication of 1956 the three-lite lamp was still depicted as the picture to the left shows14. After 1956, changes were gradually made to the design of 3-way lamps. The vertically oriented filament appeared and today (2006) the 3-way lamp is almost a necessary item in the home in order to supply different levels of illumination. In general the globe shaped bulb has been replaced with an "A" bulb.

Below are the covers for two present-day 3-way lamps. Both lamps have A21 bulbs (2 5/8" maximum diameter) and overall lengths of 5 1/8 inches.

References and Bibliography
1) "Twin-Filament Street Lights", Electrical World, Vol 102, Sep 23, 1933, pp 392-393.
2) "Three-Light Lamps Here", Electrical World, Vol 102, Nov 4, 1933, pg 581.
3) "New Lamps", General Electric Review, Vol 37, No 1, Jan 1934, pp 57-58.
4) "New England I. E. S. Learns of Lamp Developments", Electrical World, Vol 103, Mar 24, 1934, pg 451.
5) "Three-Light Lamps Fit Varied Church Needs", Electrical World, Vol 103, May 26, 1934, pg 755.
6) L. C. Twichell, "Two-Filament Lamps in New Department Store", Electrical World, Vol 103, Jun 30, 1934, pg 938.
7) "New Indirect Three-light Lamp", General Electric Review, Vol 37, No 8, Aug 1934, pg 392.
8) "Holder for Three-light Lamps", General Electric Review, Vol 37, No 8, Aug 1934, pg 392.
9) E. W. Commery, "Characteristics of Modern Residence Lighting", General Electric Review, Vol 37, No 12, Dec 1934, pg 567, 569.
10) "New 50- 100- 150-watt Three-light Lamp", General Electric Review, Vol 38, No 6, Jun 1935, pg 302.
11) "New Three-Light Lamp", Electrical World, Vol 105, Jul 6, 1935, pg 1706.
12) R. L. Oetting, "Electric Lighting in the First Century of Engineering", Transactions of the American Institute of Electrical Engineers, Vol 71, Part 2, Nov 1952, 23 pages.
13) Paul W. Keating, Lamps for a Brighter America - A History of the General Electric Lamp Business, McGraw-Hill Book Company, Inc., New York, 1954.
14) Lamp Bulletin, Large Lamp Department, General Electric Company, Application Engineering LD-1, Jan 1956, pg 25.
15) Edward J. Covington, A Man from Maquoketa - A Biography of Matthew Luckiesh, Printed by Graphic Communications Operation of GE Lighting, Nela Park, East Cleveland, Ohio, 1992, pp 77-80.