On Sun, 26 Dec 2010 01:54:30 -0500, wrote:

On Sat, 25 Dec 2010 22:36:45 -0600, z wrote:

I like doing experiments like this and I will be back as soon as my
high intensity LEDs arrive because this is my plan. We will see.
I have no problem admitting when I am wrong but I want to see it.

Go for it. I do this stuff all the time, though with indicators, not
for illumination.


OK Here you go

These are garden variety indicator LEDs (what I had handy)
There is a 270 ohm in series with 4 LEDs and a 1k pot wired as a
rheostat.
With the pot set to 0 ohms get a tad over 15M/A and the LEDs are as
bright as you can expect from these, may even be overdriven. I al
dropping 4.11v over the 270 ohm resistor.
Turning the pot down toward 1k ohms dims the LEDs quite smoothly
At 1K ohms plus the 270 I get 3.7 MA or so and I am dropping 4.8 volts
across the resistors.
http://gfretwell.com/electrical/LED%...experiment.jpg

Now, scale that to your 120V application.

I agree it is not exactly linear but I also do not understand how this
small variance makes any real world difference since most of the
voltage is still being dropped across the LED string. You certainly
would have a hard time seeing it on your electric bill.

It will *not* be a small variance when you add another 30 or so in series and
a smaller ballast resistor. Add in the sine wave excitation and you're going
to find your results don't match your experiment very well.