On Fri, 24 Dec 2010 17:06:06 -0800 (PST), Red wrote:

On Dec 24, 11:50*am, "
wrote:


Yes, you are correct, except that the LEDs have to have a "threshold"[*]
voltage to light at all. *If the dimmer is triggered when the AC (sine wave)
is too low the LEDs don't light. *The range of adjustment will be very small.
[*]as others have pointed out, this isn't an on/off thing but is highly
nonlinear

* I think the key is how the current source is constructed. Limiting
the power lost there is important.

Yes, this is a very expensive thing to do, compared to a *cheap* Triac dimmer.


Note: http://joby.com/store/gorillatorch/switchback

Joby makes several models of quality dimmable LED lights, but as you
said they are not cheap. The one in the link will dim thru a range of
5 - 130 lumens, mostly linear and without flicker. I have one and it
works great. I have no idea of the circuitry they use to dim the LED
and I'm not going to take it apart to find out.
This response is just to let the doubters know that the technology to
dim LED's is real and available.

Sure dimming LEDs is possible, and actually not all that hard if you start
with DC (the unit you linked is battery powered). Doing it from the AC line,
cheaply and efficiently, is more challenging. It's easy to do sloppily, but
then there is no gain over an incandescent bulb.