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I'm using a Pi to drive a Fadecandy board to light up a varying-length string of RGB LEDs in different, pulsating colors. I've been successful, however one snag I ran into along the way was programmatically defining the LED colors in RGB.

I copied the Fadecandy example program measuringstick.py (which makes every 10th LED green and the rest white) and tweaked it to create a rainbow of colors instead. Wrote the program into /etc/rc.local, rebooted the Pi, and noticed that my colors were completely off! After a half hour of messing around, I realized that defining the colors in GRB instead of RGB gave the correct result. In other words, if I want an LED to be bright red I have to define its color as (0,255,0) instead of (255,0,0).

Is this a normal thing with LED pixels? All of the example code was written in RGB, so I assume that GRB is not normal. Can someone explain to me what's going on? I'm more curious than anything at this point.

(Sorry I don't have any code to show you. My collaborator has the lights/Pi with him today)

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    It depends on the specific led's the majority are RGB but I have some that are GRB. That is why I always test with just (255, 0, 0), (0, 255, 0), (0, 0, 255),
    – Steve Robillard
    Oct 1, 2015 at 16:06
  • There are dozens of different RGB LED strips. I'd say the most likely explanation is that yours are written in GRB order rather than RGB.
    – joan
    Oct 1, 2015 at 16:07
  • Good pro tip about testing, @SteveRobillard joan I had no idea this was a thing! Good to know...
    – Ryan Schuster
    Oct 2, 2015 at 14:56

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If you buy cheap RGB LED's from china, you can get GRB mixed with RGB's. Happend to me a few times. Then I decided to pay a bit more to be sure I get what I order.

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    Hah! Good to know. I inherited all of this equipment but I guess not I know to check for GRB vs RGB.
    – Ryan Schuster
    Oct 2, 2015 at 14:55

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