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A three-way incandescent light has two filaments: dim and medium. Each filament has a separate contact on the bulb"s base. The brightest light level is provided by energizing both simultaneously. When energized, each filament is driven at the mains voltage, so applying that voltage to a standard LED bulb will cause it to produce its rated light output.
You"ll probably find that (because the bulb"s base is missing a contact), you"ll have an "on, off, on, off" pattern as you rotate the switch, instead of "dim, medium, bright, off" like with a 3-way bulb.
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edited May 16 "11 at 19:46
answered May 16 "11 at 19:39
Niall C.♦Niall C.
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3 Way LED bulbs finally do exist now: http://store.earthled.com/products/switch-switch3-way-led-light-bulb
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answered Mar 20 "13 at 15:56
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I am terribly sorry to contradict two others replying to this question, but I wish to set the record straight on what may be a misunderstanding of the original question.
The question is not about a 3-contact socket which require a 3-contact bulb (with two separate filaments).
The manufacturer"s statement: "For incandescent bulbs only" or "Not for compact florescent bulbs" does not mean that you must avoid LED bulbs. That statement may simply mean that the manufacturer failed to account newer LED bulbs...
A 3 way touch switch works by offering a reduced brightness level, but it uses a standard 1-brightness bulb. It achieves the cut-back in illumination by either reducing the voltage or "chopping" the wave form (this is more typical). One very cheap method of dimming a single brightness bulb is to simply skip every other 1/2 wave, as if a diode were inserted in series. But this can produce noticeable flicker and can also cause compact florescent bulbs to overheat.
But to the point: The original writer asks if one can place an LED bulb into a lamp that has a 3-way touch control. The answer is: "It depends!...You must test it!" Here is the reason...
First, LED lamps are typically marked dimmable or NOT dimmable. As of 2014, most screw in replacements from the major brands (CREE, GE, Philips) are dimmable, if they are "equivalent 100 watts" or less. However, they require a dimmer than chops the leading or trailing edge of the waveform. As an example, they require a more expensive wall switch dimmer than the standard incandescent dimmer ($20 as opposed to $10 for a comparable model). So part 1 of my answer is to use only an LED bulb that is marked "dimmable".
But part 2 is trickier...
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If you purchased a lamp that says to use incandescent only, you should test it with your LED lamp. In my Hampton Bay model 494 595 upright accent lamp, one brand of LED bulb shines only at full brightness, yet produces an annoying hum at the dim step. But another LED bulb works just right, at half and full brightness. I would mention the bulb model, but they are store brands, and Home Depot is known for switching suppliers or MFG series without changing the SKU or model number. Therefore, these details would be short-lived.
The bottom line, is that (a) It is likely that the touch-dimming circuit is compatible with many LED bulbs, and (b) You must still test the bulb to see if it dims. If it does (and if it does not make noise), it is very likely that the electronics in the bulb "realize" that a dimming circuit is being used, and so the bulb is cooperating by doing the dimming within its own circuitry. Therefore, you should be fine!