Bob Vila Radio: Is It a Three-Way Lamp Socket?

The next time you return home from the flea market with a lamp under your arm, here's how to tell whether or not its socket can take a three-way bulb.

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How can you distinguish between a standard lamp socket and a three-way? It’s simple! Standard sockets have only two electrical contacts. The hot contact, a small metal tab, sits at the bottom of the socket, while the negative contact is the threaded metal shell (the one the bulb screws into).

Three-Way Lamp Sockets

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Listen to BOB VILA ON STANDARD SOCKETS or read the text below:

Three-way sockets look very similar. The difference is that next to the metal tab at the bottom, there’s a third contact—a bit smaller than the metal tab and set slightly off center. That extra contact matches a small ring-shaped contact on the bottom of a three-way fluorescent bulb. Such bulbs are characterized by having two filaments, not one. When you twist the switch on a three-way lamp, the first click illuminates a single filament. The next click deactivates the first and illuminates the second, this one with a somewhat higher wattage. The final, third click illuminates both filaments at once, giving you the brightest light.

If you’re looking to trim your electric bills, you might want to check out compact fluorescent or LED bulbs, many of which are made expressly to work in conventional three-way fixtures.

Bob Vila Radio is a 60-second home improvement radio tip of the day carried on more than 186 stations in 75 markets around the country. Click here to subscribe, so you can automatically receive each new episode as it arrives—absolutely free!