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A 3-way lamp, also known as a tri-light, is a lamp that uses a 3-way light bulb to produce three levels of light in a low-medium-high configuration. A 3-way lamp requires a 3-way bulb and socket, and a 3-way switch.
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]