On Dec 26, 2:54*am, wrote:
On Sat, 25 Dec 2010 22:36:45 -0600, 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

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.

You should see the PWM method. brightness is variable from next to
nothing to full bright. They also retain their color while white
lights turn yellow using your method.

Jimmie