Is it possible to use an LED bulb in a 3-way light fixture? Will all three work?
Unless you have a 3-way LED bulb (and a quick search indicates that they don't exist yet), it will light, but at the brightest light level.
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.
3 Way LED bulbs finally do exist now: http://store.earthled.com/products/switch-switch3-way-led-light-bulb
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...
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!
Philip Raymond Massachusetts
are you talking about a 3-way switch in a desk lamp? if so, that will be fine. those work by adding a second set of contacts in the base of the socket that if the bulb is a 3-way bulb then it touches those extra contacts. those contacts provide exactly the same voltage as the other contacts.
in short, this will not be a problem.
Apparently there is now a three way LED bulb http://www.cnet.com/products/cree-three-way-led-bulb/
In my slightly frightening experiences, No you can't put a regular Or dimmable LED bulb in a 3 way lamp socket. I've tried it with two different bulbs from Osram Sylvania that claim they are dimmable. The first one shot lots of sparks and fire upwards and scared me. I tried it in another 3 way lamp (not too scared, just dumb?) socket and it did it again to a lesser degree. No doubt a lesser degree since after that try I looked at the base and it had a large hole that spread to almost half of the base. This ruined both lamp sockets. I called Osram Sylvania and a man sent me an envelope to send it to him and he sent, eventually, two checks made out to any retailer of their products. One for $20 and one for $10. That bought me another LED bulb, two CFLs and two new sockets. By the way, the man asked me if I'd put it in a 3 way socket and I told him I had. I tried the new LED in a 3 way socket and it shot sparks up again, without trashing the socket this time. I took that bulb back to the big box store and got an on / off socket and a dimmer switch that you plug the lamp into. Now, after reading the comments, I see that I'll probably be taking the dimmer switch back, as it's not one as described above. Fortunately they now have 3 way LED bulbs, though they are costly. One would think there'd be a warning on packaging, since the Osram Sylvania guy knew about the problem. Or maybe it's just a problem with their products. These were 3 way turn knob switch sockets, like I presume the original poster was talking about since he didn't say anything about a touch control.
This Q&A from GE, regarding CFL bulbs, should apply for LEDs as well: http://www.gelighting.com/na/home_lighting/ask_us/faq_compact.htm#three_way
Basically, unless the bulb was designed to work in a dimmed context, and says so on the package, you should NOT use it with a dimmer or in a three-way fixture.
HEHE I made my own 3 way LED. I had a popped CFL and carefully removed the curleycues to get the base. I then put in two LED drivers (from 120VAC) and two LEDs which were 5 watt and 2 watt. I think luxeon stars. It works, albeit not as good as I would like. The LED drivers are tiny and did fit into the CFL power supply base.