Red + Green + Blue = White. But how many of each?

[wakibaki]

Does anybody know what mix of LEDs you need to get a reasonable white?

I mean like 3 Red + 1 Green + 2 Blue. Or is it just 1:1:1?

The datasheets show applications like LCD backlights with variable CT, but these control the output of the individual LEDs.

I'm more interested in combining the light of a bunch of LEDs running full bore, or close to it.

This is obviously not a straightforward question, but I wondered if anyone might know a rule of thumb that would get me on the right track.

w

 

[defusion]

I guess you need to find out what intensities in the three colours white consists of, and find out how bright each of the LEDs are. Then do some math, and you know.

 

[KnOeFz]

I think you'll find this RGB configuration by Bombelman interesting:
http://candlepowerforums.com/vb/showpost.php?p=2001954&postcount=7

 

[wakibaki]

I guess you need to find out what intensities in the three colours white consists of.... Then do some math...

Yesyesyes. Math.

OK, my brain clicked in. I remembered that white means that there is a constant power spectral density, i.e. the same power in any given bandwidth around any central frequency. So you need to convert back from lumens to mW and have equal mW at the blue, green and red spectral sensitivity peaks of the eye at 419, 531 and 558 nm. I guess if the colour/frequency isn't quite right you can figure an adjustment from the sensitivity curve. As a rule of thumb you need 1 each R,G,B of the same power if the efficiency in mW/W is equal.

Does anybody know how to calculate the effective colour temperature?

Good pic of those 3 mixed beams.

w

 

[Ken_McE]

Does anybody know what mix of LEDs you need to get a reasonable white?

To start, I suggest you try 3 red, 3 green, and one blue. We don't use blue that much.