3-way lamp
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A 3-way lamp, also known as a tri-light, is a
In 3-way incandescent light bulbs, each of the filaments operates at full voltage. So unlike incandescent bulbs controlled by a dimmer, the color of the light does not change between the three steps of light available.[citation needed] Lamp bulbs with dual carbon filaments were built as early as 1902 to allow adjustable lighting levels.[1]
Certain compact fluorescent lamp bulbs are designed to replace 3-way incandescent bulbs,[2] and have an extra contact and circuitry to bring about similar light level. In recent years, LED 3-way bulbs have become available as well.[3]
3-way bulbs
A 3-way incandescent bulb has two filaments designed to produce different amounts of light. The two filaments can be activated separately or together, giving three different amounts of light. One common 3-way incandescent bulb is the 50/100/150 W. It has a low-power 50 W filament and a medium-power 100 W filament. When they are both energized at the same time, 150 W of power is delivered, and a high level of light is produced. Usually screw-base 3-way bulbs fit into regular Type A sockets (E26D after ISO 60061-1:2014). Larger 3-way bulbs (up to 300 W) have a larger "mogul" base (E39D). These 3-way bulbs can also come in spiral-shaped compact fluorescent lamps.[2]
3-way sockets
A standard screw lamp socket has only two
A 3-way socket has three electrical contacts. In addition to the two contacts of the standard socket, a third contact is added. This contact is positioned off-center in the bottom of the socket (contact two in photo). This extra contact matches a ring-shaped contact on the bottom of a 3-way bulb, which creates the connection for the second filament inside the bulb. A problem of these devices is that the ring contact of the socket (contact two in photo) digs into the lead seal on the lamp bulb's contact ring and this connection tends to fail early (sometimes in months), leading to intermittent flashes, popping noises, and loss of power to the low wattage filament as the lead seal on the bulb's ring alternately melts and solidifies.
The center contact of the bulb typically connects to the medium-power filament, and the ring connects to the low-power filament. Thus, if a 3-way bulb is screwed into a standard
A key switch 3-way socket has the switch incorporated in the lamp socket and requires no external wiring between switch and socket. This would be typical in a 3-way floor-standing
3-way, 2-circuit switches
The switch used to control a 3-way lamp is usually a
Lamp function | Switch one | Switch two |
---|---|---|
Off | Off | Off |
Low, lamp one | On | Off |
Medium, lamp two | Off | On |
High, lamps one and two | On | On |
See also
References
- ^ US 931807, "Incandescent Lamp"
- ^ a b Matthews, Mike. "How a 3-Way CFL Switch Works". HomeGuides.SFGate.com. Hearst Newspapers. Retrieved March 21, 2022.
- The Spruce. Retrieved January 7, 2023.
- ISBN 0-07-013932-6.