LED colour mixer for Art Class

Hello Readers

I am interested in using a colour mixing device as an educational tool in my art classes. The fact that I teach art should already hint at my problem; lack of skill..

I have done quite some research already, and have ordered RGB LED's from superbrightleds.com. I have also roughly figured out how I should wire the thing. HEre's my plan:

The RGB led has 3 channels (only one blue chip), so I will use resistors to limit all three channels to their maximum current. Then I will use 'variable resistors' to limit further the brightness of the channels.
I ran into a couple of things I havent been able to figure out: The spec sheet on superbrightleds.com tells me that the absolute max rating for the LED is 100mW power consumption. But it also lists typical current for each channel at 20mA. If I add three channels at full power together, the total power dissipation is well above 100mW. What am I doing wrong? And if so, what is a lower current value that would give acceptable brightness?

Spec sheet: http://www.superbrightleds.com/TriColor%20LED.htm

Another question concerns how much resistance I need from the variable resistor to completely black out the LED.. At what point does an LED stop giving off light. IS there a wide margin or not?

Any other suggestions are welcome, as are any links that you might have for me. Thank you for your patience,

TTH

I don't think you can completely black out a LED with a pot (=variable resistor) and use the same pot to regulate the brightness, it's just not accurate enough. Maybe you can try a simple transistor based variable voltage source (= 1 pot and 1 transistor for each color). You can also buy a Sauce lightwand from colorkinetics... /ubbthreads/images/graemlins/smile.gif

You might take a look at This article. You might also consider purchasing (For yourself if not for teaching /ubbthreads/images/graemlins/wink.gif ) something from the fine people at Color Kinetics

Why not save your money and just use some gel filters and a bright white light source like a projector. I made some filters with some clear mylar and a red, green, and blue sharpie pen.

I would guess that the max 100mW power rating means you'll have to scale back the brightest output you're going to produce. Since human eyes are less sensitive to blue light to begin with, I would set up the circuit to allow the blue to run at full power, and reduce the max for red and green. With the red and green limited to 5mA each, you'll be within the 100mW max and you'll still have enough of each to produce a balanced white using the weak output of the blue.

As for the pots - this will be a trick, finding one with the fine resolution you'll need...

You should probably use several LEDs wired in parallel just to give you more dynamic range.