Reducing power of halogen lamps

I have a bedside lamp with a 100W halogen lamp which runs directly off 110V. In the base of the lamp is a small rotary switch about 3/4" in
diameter. It has three positions: Full intensity, reduced intensity and off. No other parts are discernible.
The question is: How does the lamp achieve the reduction in light intensity (about half)?
I actually know the answer because I took the switch apart but when I was looking for it before on Google etc. I could not find it.
I am posting here to see how widely this trick is known.
Oh, and the lamp is *metal*.
Michael Koblic, Campbell River, BC
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snipped-for-privacy@gmail.com wrote:

A diode. Cut out half of the AC cycle and get reduced brightness. Very, very common, indeed there are/were little socket insert disks made that you stuck in a light socket to save power.
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Pete C. wrote:

A friends son has a filament lamp which has 3 intensities and off and cycles between them when you touch the metal lamp base itself, no switch just contact. How would that be done.
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David Billington wrote:

Simple touch switch controller, uses several fixed levels of regular triac phase control for the dimming. You can buy the control module for like $5 to add to any lamp that has some metal surface you can use for the touch switch.
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On Tue, 28 Feb 2012 01:38:18 +0000, David Billington

Capacitive touch switch and a "tri-lite" bulb.
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    [ ... ]

    First off -- the base is serving as an antenna to pick up stray AC noise from the room, and when you touch it you increase the level to above a pre-set threshold. It then waits for the noise to go down below the threshold and back up again to switch to the next.
    If the bulb is not a three-way bulb (two filaments of different wattages used one at a time or both together), then it probably has a transformer with its secondary in series with the AC line to the lamp, and switched to either aid, oppose, or switched out of the circuit entirely. This should give you three brightnesses.
    Or, another (cheaper) way to get the brightnesses (with the same switching sensor for the touch base trick) would be to change the width of the part of the AC cycle which is allowed to reach the lamp -- like a dimmer with three steps instead of continuously variable. Since that is cheaper, it is probably how they went. Try picking it up and judging by the weight whether it has a transformer in the base.
    Enjoy,         DoN.
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Unlike a regular tungsten filament lamp, a halogen lamp actually will burn out much more quickly at reduced power if the temperture of the envelope drops below the point needed for the halogen cycle. http://en.wikipedia.org/wiki/Halogen_cycle#Halogen_cycle
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    The way I would do it is to put a diode in series with the lamp on the low-intensity setting. I would guess that it is possible that the diode could be inside the switch housing.

    That is good -- so many are plastic these days. :-)
    Enjoy,         DoN.
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wrote:

Correct. A dirt-cheap 1N5404, hidden inside the switch. Half-wave rectifier properties etc. have already been mentioned.
I thought it was a neat trick. A resistor achieving the same thing would have to be of the order of 17W or so.
BTW neither the people who sold the lamp nor the experts in the two specialist electrical shops knew the answer.

Purely so I don't have mark the thread "OT".
Michael Koblic, Campbell River, BC
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Many semiconductors wouldn't exist if not for deposited forms of various metals.. nor would many forms of illumination devices.
So generally, still on topic even if by trace amounts, which is far greater than many of the bullshit hero worship/hate posts appearing every day.
--
WB
.........


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    And the resistor would be sensitive to the wattage of the bulb installed -- assuming that it was a kind where various bulbs would fit it. And the switch would probably get rather uncomfortably hot to the touch after a while of operation. :-)

    Of course not. They aren't members of this newsgroup, where people care how and why things work.
    Enjoy,         DoN.
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There's an old parlor trick with two switches and two bulbs wired in a series loop where each switch controls a bulb independently.
http://img517.imageshack.us/img517/7576/trickcircuit1tb.jpg
http://img291.imageshack.us/img291/1263/circuit25jw.jpg
You build it with porcelain-base knife switches and lamp sockets each on a separate small wood block, connected with a single strand of solid or clear-insulation speaker wire.
With both switches open, both bulbs are off. Close either switch and its bulb lights even though the other switch is plainly open -- that's the reason for using knife switches. There is enough open space under the porcelain base for the diodes, which the wood blocks keep concealed. Don't show it to technicians who might carry screwdrivers (like me) and ask to disassemble it.
No one ever notices that the bulbs aren't at full brightness.
I don't have a photo of mine, I took it apart because it is so dangerous.
jsw
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Jim Wilkins wrote:

AKA: "The Impossible circuit". You could build one today with LEDs and a wall wart.
--
You can't have a sense of humor, if you have no sense.

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Jim Wilkins wrote:

...
Cute. You could power it with a 24v transformer & use 12v bulbs, for full brightness and a safe circuit.
Bob
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On Wed, 29 Feb 2012 09:07:23 -0500, "Jim Wilkins"
[...]

The concept of dangerous electrical circuits brings back all kinds of nostalgic memories.
When I worked for a film company (a 1000 years ago) there were two favorite ways of boiling water for coffee on location:
1) A large wattage resistor connected directly to mains used as an immersion heater. Note: The mains were 220V.
2) A cup with two plates on top of each other but not touching, each connected to mains. Pour water directly into the cup, plug in. This arrangement boiled water literally in 3 seconds.
Yet the only mortality I remember was work-related: A broken cable under water.
Michael Koblic, Campbell River, BC
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snipped-for-privacy@gmail.com wrote:

One of our high school projects was a wiener cooker comprised of a plastic shoebox, a micro-switch and rows of nails to impale the ends of the unfortunate wieners. Plug it in and wait for the hot dogs to cook.
Worked great.
--Winston<-- I don't figure they'd do that today.
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On Thu, 01 Mar 2012 18:12:36 -0800, the renowned Winston

http://www.flickr.com/photos/oskay/713401829 /
Best regards, Spehro Pefhany
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snipped-for-privacy@interlog.com Info for manufacturers: http://www.trexon.com
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The observant Spehro Pefhany wrote:

That is Great!
Next: Vienna sausages, for the low power version.
--Winston
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On 3/1/2012 8:41 PM, Winston wrote:

<
http://www.youtube.com/watch?v=mh7VHcuaPCg&feature=fvwp&NR=1

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dpb wrote:

Electricity, is there no problem it can't solve?
--Winston
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