RGB LEDs and color balance?

I bought a couple of 5mm RGB LEDs at my local parts supplier, and I've been really disappointed with the "color balance," namely that with all three colors lit at max (and run through a diffuser), it really looks nowhere near white. Tuning the colors to get it to white (or a reasonable approximation thereof) is annoying, plus it significantly reduces the overall brightness of the LED.

I was wondering if anyone had any experience with the RGB LEDs available from Sparkfun (these) or from Superbrightleds.com (these), and could tell me if the balance is any better. The Sparkfun ones look like they blend to produce a good white from their picture, but it's hard to tell.

I'm not looking for perfect color matching; what I would like is something that produces a reasonable approximation of what one would see on a screen if I output the RGB values as PWM signals, especially for the key points of all on (white) and any two on (magneta, cyan, and yellow).

Has anyone used these (or any others) and care to share their experiences? Thanks!

I have the Sparkfun triple-LEDs, and I’ve been playing around with them for a while (messing with Arduino and pwm and stuff). Overall, I’m quite happy with them.

I’ve made no attempt at perfecting their white-balance, but they definitely don’t output a perfect white when all on. On the other hand, any two on produces great cyan, magenta, and yellow. Yellow is not quite as good as the cyan and magenta, but still fine IMHO. Red, green, or blue by itself is perfectly color-accurate, of course.

When viewed from the side, the LED’s color is good, but when the LED is pointed at the wall or something, you can distinctly see three circles of red, blue, and green (I think that’s the actual order).

If I have time, I’ll try different values to subtract from each color to see if I can get a better white.

Thanks for the information, dylpkls. It sounds like the Sparkfuns are a definite improvement over what I've got, which produces a definitive blue when all three are on, and a slightly yellow-tinted green instead of yellow. I'd love to hear what you have to do to get it to be whiter, if you get the chance.

I haven't tried getting a better white, and I don't think I will, but my approach would be to start with all three at 255, then subtract a little as needed to make it look better. For example, if values of 255-255-255 are "too red," I might try 240-255-255.

One big problem with 3 color LED's is that the 3 different colors are not at all the same intensity, and the 3 colors als do not always "point in the same direction".

One big problem with 3 color LED's is that the 3 different colors are not at all the same intensity, and the 3 colors als do not always "point in the same direction".

Well, the diffuser takes care of the fact that the colors don't "point" in the same direction (at least, it takes care of it enough for my purposes). I guess the fact that the intensities are different is what's causing my problem. Unfortunately, the luminosity ratings on datasheets don't mean anything to me, and from what I can see the green and blue are usually much brighter than the red, although sometimes green is the brightest and sometimes blue is. The differences between them seems to vary a lot, too.

It looks like I'm just going to have to pick a manufacturer, order some, and hope for the best.

If you find some good ones please let us know.

And good luck

I ended up buying some from superbrightleds.com (part RL5-RGB-D, diffused lens, common cathode). I'm pretty happy with them; most importantly, they're vastly superior to the ones I had before (purchased from a local store, manufacturer and part number unknown). I can't compare them to other sources, but I can't complain, either.

What you might want to do is setup a test circuit with variable LEDs for each of the three LED chips. You'll have to vary the current (at the same voltage) through the different LEDs because they have different luminosity outputs. Once you achieve the balance via resistors, you can fix that circuit and use PWM to do the blending.

I bought 100 RGB leds off ebay and when coated with white paint they look flawless.

A little off topic - but if I have a choice of common annode or common cathode which one would I want - I probably want to use them in a 3D color cube of some kind.....

I found a 50 pack of common anode on eBay for a really good price.

A little off topic - but if I have a choice of common annode or common cathode which one would I want - I probably want to use them in a 3D color cube of some kind.....

It really depends on what you're using them for. The setup and PCB that I was using required a common cathode, and wouldn't have worked otherwise; then I overhauled my design, and it looks like I'll need to get a set of common anodes, because the new setup won't work with CCs.

It depends on whether you're controlling brightness via something that sources current or sinks it; if you're controlling by sourcing current, you'll want common cathodes (so that each anode can be connected to the current source), and if you're controlling by sinking current you'll want common anodes (so that each cathode can be connected to the sink). (Disclaimer: I sincerely hope I didn't get that backwards, but I'm not ruling out the possibility! ;) )