three-way bulb

[three-wey]

noun

1. a light bulb that can be switched to three successive degrees of illumination.

Example Sentences

If they are not available, “a three-way bulb works nicely to control the level of light in a space,” Underwood says.

Read more on Seattle Times

And if your lamp has a three-way bulb, be sure to buy a replacement socket of the same style.

Read more on Washington Post