Calculating light output from RGB leds

[Frobe22]

I am a bit stuck trying to calculate light output from a RGB led compared to regular white leds. Adding the intensity values is probably not the correct way to do it?
My purpose is to try to replace some rgb leds with white, and I want to have the same brightness.

[PhantomPhoton]

Good question.
I'm no expert, only guessing here...
But I think adding the individual color values will give accurate numbers. It may not appear much brighter than a single color but thats how our eyes handle light. What's the apparent difference in brightness between 1 flashlight and 3 equal flashlights? The second and third to make it seem a bit brighter if you went into a dark room and compared 1 on vs 3 on but don't make it appear 3 times brighter than the first.
Anyone more knowledgeable out there care to chime in? I'm interested too.