How do 3-way light bulbs work? How do the bulbs "know" @ which intensity to shine?

Answer 1

From How Stuff Works:

"A three-way bulb has two filaments in it. The next time one burns out, carefully open it (for example, wrap it in a towel and hit it lightly with a hammer) and you will see the two separate filaments.

For the lowest setting, one filament comes on (it might be a 50-watt filament). For the next setting, the second filament comes on (it might be a 100-watt filament). For the third setting, both come on, for (in our example) a total of 150 watts.

Look also at the end of the bulb's base -- you will be able to see how the lamp controls the two filaments. "

Also:

"A three-way bulb has two filaments of different wattage -- typically a 50-watt filament and a 100-watt filament. The filaments are wired to separate circuits, which can be closed initially using a special three-way socket.

The switch in the three-way socket lets you choose from three different light levels. On the lowest level, the switch closes only the circuit for the 50-watt filament. For the medium light level, the switch closes the circuit for the 100-watt filament. For the brightest level, the switch closes the circuits for both filaments, so the bulb operates at 150 watts."

Hope this "brightens" your day!

Answer 2

they have filiments, the little wires inside of them. as you change the setting on the lamp either one or two recieve current,( they come on or are off)

Answer 3

They have a variable resistor in them something like the dial on an oven that sets the temp. You set how much electridity goes through.