[sdiy] calculating resistance to match brighness across different colours of leds?

[np]

Scott Nordlund wrote:
> The eye is more sensitive to green, but I don't think it would be very easy to tell which is brighter just by looking at it.
>
> Maybe you could combine the light of both and adjust for a reasonable yellow color.
>
>   
The percieved brightness depends not only on wavelength, but on the 
luminosity and the wavelength perceived by the surrounding perceptors 
ect. A highly complex thing. There is one good thing about the eye and 
the perception though: If you're close in brightness the eye will equal 
out the differences for you.


As a rule of thumb I can give you the relative sensitivities for CRT 
phosphors. If your LED wavelength are in the same ballpark, and you want 
the LEDs to be relative bright it should be okay.

Sensitivity for blue: 0.144 green: 0.587 red: 0.299

E.g. if you want a blue light to be as bright as a red one you need 
0.299/0.144 times the luminous intensity from the blue source to get the 
same percieved brightness.


Cheers,
  Nils.