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Topic: R, G, and B LED Voltages/Brightness? (Read 2379 times) previous topic - next topic

R, G, and B LED Voltages/Brightness?

With the Color-changer's example LED PCB, what value LCDs should be used?

I'm guessing >75mA, High Brightness LEDs, with the Red ones at half the voltage of the Greens and Blues?

I'd also assume for an even color, I'd want LEDs with equal millicandela (Light output) rating and a fairly wide viewing angle. I'd probably go with a diffused lens to produce a more even color as opposed to a number of single points of light.

Background: I'm currently thinking of a behind-monitor screen lighting, similar to some flat-screen TVs which produce ambient light based on the dominant color currently on the screen (IE, it'd take the average R, G and B color of the screen every X amount of seconds... It shouldn't be that hard to script under Linux.)

Thanks in advance!
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Re: R, G, and B LED Voltages/Brightness?

Reply #1
You will definitely need a diffuser, the individual LEDs don't always blend well.

I used bulk 20ma ~14000mcd LEDs from beshongkong.com  (watch out, they sold my email to a million spammers - I now block besthongkong@whereisian.com). They had a pretty high forward voltage on the blue and green, but the reds were standards. One thing to note is that MCDs go down when the viewing angle increases, and MCDs seem to mean different things for different colors (could be wrong about that last point).
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Re: R, G, and B LED Voltages/Brightness?

Reply #2
Spectral sensitivity for the eye varies (yellowish-green good, less for red, and poor sensitivity to blue) so you may need more of one led to achieve a specific colour you have in mind.

Re: R, G, and B LED Voltages/Brightness?

Reply #3
Thanks, Ian and Nexus.
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Re: R, G, and B LED Voltages/Brightness?

Reply #4
I wonder if it could be used to drive multiple RGB LEDs instead of multiple sets of individual LEDs... That'd solve the color balance issue.

I'm thinking common anode RGBLEDs, with the anode powered by the +12V pin and a cathode leg on each of the R, G and B pins.

There seem to be some reasonable prices for bulk RGB LEDs on eBay... Even if they're relatively anemic and I have to use 2 or 3 in the place of 1, I could always run parallel and serial circuits of them to stay around 12V.

(I also assume you could just sand the surfaces of clear-bulb LEDs to get 'diffused' ones ;))
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