On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at all.
The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to current-share
across the LEDs. Counting on the internal resistance of a battery is really
****-poor.

With just the batteries in there the lights are pulling about 244ma
(they are fairly new batteries)
This is hurt your eyes bright.
I put my 1k pot in there and even all the way off I am dropping .05v,
current around 211ma.

I assume you mean, "all the way *ON*", as in "zero" ohms (the wiper resistance
is about 1/4ohm).

The slightest movement of the pot, only putting
a couple ohms in there rapidly starts dropping the current. Somewhere
around 900 ohms we are at 3ma, dropping 1.3v
and the light is "indicator bright".

1.3V/.003A = 433 ohms.

OK so back to the junk drawer for some smaller resistors
With 10 ohms in there it is dropping 0.8v 77ma

Ok.

the light is noticeably
less but still pretty bright. When I double that with 20 ohms the
light dims quite a bit, current drops to 48ma and voltage 0.94v

You can already see that it's nonlinear and you're using a DC source.

I guess somebody has to crack open a 120v LED bulb or just do an
experiment like this to see how they work but I know what I need to
know about a low voltage setup like I want to make. I am thinking a 25
or 50 ohm pot will do the deed for me.

I thought you wanted an AC powered light? If all you want is to dim a
low-voltage DC string, PWM is the way to go. It's pretty easy. There are
cheap chips to do this automagically.