Can you use a normal light bulb in a 3-way socket?

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Using a standard bulb in a 3-way socket

Can you use a normal light bulb in a 3-way socket? - Contacts on 3-way light bulb
Image from user:Icysubdweller, CC BY-SA 3.0 via Wikimedia Commons


This article is about whether you can use a normal light bulb in a 3-way socket.

In brief the answer is yes. However it will only work on certain of the sockets settings.

To explain we first look at how 3-way sockets work. Then we show how 3-way bulbs work. Finally we see what happens if you put a normal bulb in a 3-way socket.

How Does a 3-way Socket Work

Let’s begin by looking at how 3-way sockets work. A normal socket only has two connections to the light bulb. These are the neutral connection and the live connection. Whereas a 3-way socket has 3 connections. In this case a neutral connection, a low wattage connection and a medium wattage connection.

Note that when we say socket we likely mean a desk lamp or a floor lamp. Rather than a socket that is hanging from your ceiling.

That said, on your 3-way lamp there is a switch with 3 positions. Let’s call them low, medium and high. In the low position the lamp connects power to only the low wattage contact. Similarly in the medium setting only the medium contact has power. And in the high setting both contacts are powered.

How Does a 3-way Bulb Works

Incandescent 3-way bulbs

Incandescent light bulbs are the old style bulbs with a metal filament. When a current passes through the filament it gets hot. And this produces light. However around 90% of the power turns into heat. For this reason they are very inefficient.

In an incandescent 3-way bulb there are 2 filaments. Normally a 50 watt filament and a 100 watt filament. The low contact in the socket powers the 50 watt filament. Similarly the medium contact powers the 100 watt filament.

So, if you put the switch in the low position you get 50 watts. And in the medium position 100 watts. Also the high position powers both filaments and you get 150 watts. Thus, 3 different light levels. And that is why it is called a 3-way switch, lamp or light bulb.

LED 3-way bulbs

Firstly LED stands for Light Emitting Diode. Secondly, LEDs are small pieces of semiconductor. The same semiconductor technology as is in our phones and computers. Next, like incandescent filaments they emit a light when a current passes through them. The difference being that in an LED light bulb there are 3 separate LEDs. One red, one blue and one green. Combined they produce a white light. recent advances have produced a single LED that produces white light. In fact it is actually a blue LED a phosphor coating. The coating convert the blue light to white light by a process called fluorescence

So how do 3-way LEDs work? Basically the LED bulb turns on more LEDs depending on the which connections are powered. For example, if the bulb has 21 LEDs inside. The lower setting powers 7 LEDs. Then the medium setting 14 LEDs. Finally the high setting powers all 21 LEDs. Giving 3 different levels of light.

Note that the newer vintage style LEDs actually have something that resembles a filament. Though it is in fact a strip of LEDs on a piece of metal. This technology allows for the manufacture of a 3-way LED bulb that works in a the same way as an incandescent bulb. That is, the switch turns on one, two or both filaments.

How a Normal Bulb Works

E26 Screw Cap on LED light bulb

Have a look at the screw end of a light bulb in your house. It has 2 connection. Firstly the metal screw which is the neutral connector. Secondly the central metal connector which is the live connection. In a normal socket power goes to the live connector. From there it runs through the bulb causing light. Then back out the neutral connector. For incandescent bulbs the power goes through the filament. Whereas in LED it powers up the LEDs. In both case it generates light.

So Can You Use a normal light bulb in a 3-way socket?

Look at the picture of a 3-way bulb at the start of this article. There are 3 connections. Neutral, medium and low. A normal light bulb only has two connection. These line up with the neutral and medium connection in the 3-way socket. What this means is that when the socket is switched to medium or high, power flows through the bulb and you get light. Conversely, the low light connector does not match up with a normal bulb so you get no light in this setting.

So a 3-way switch would have the following output as the switch is rotated.

Off >> Low >> Medium >> High >> Off

However if you put a normal bulb in the socket you would get

Off >> Off >> On >> On >> Off

So, can you use a normal light bulb in a 3-way socket? Well yes. You will get a strange on-off sequence but it will work just fine. But you will only get one level of light.

As a final note remember that 3-way sockets are not dimmers. In all settings they provide the full power to the light bulb connector.

If you are interested in a real 3-real bulb for your 3-way lamp then see are article on Best 3-Way Bulbs.