On 2012-02-28, David Billington wrote:
Pete C. wrote:
wrote:
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 am posting here to see how widely this trick is known.
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.
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.
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.
--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. |
http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---