Yes it is true that you can't ever get more light / watt than theoretical green light.
Ok, was never arguing this point, about theoretical efficiency, but instead, ignoring theory, what is actually true in practice. I'm still waiting for the old timer heavyweights to chime in, but my understanding is no one is spending any R&D of consequence on the efficiency of green LEDs, mostly due to the fact that in practice, green LEDs are far less popular than white LEDs. Most of the advances in LED efficiency in recent decades has been in getting white LED's more efficient, leading to some unexpected (to those only considering theory) anomalies in practice, such that today's white LEDs are more efficient than, say, red LEDs, when theory and physics tells us otherwise. The point being is that far more effort is going into making existing, i.e. real, actual, white LEDs more efficient. We may never have the theoretical 100% efficient green LED, because no one really cares, no one needs them, thus no one is working on that. White LEDs, however, are very popular and there is an enormous interest in getting them as close to their theoretical maximum efficiency as possible. Thus it is very very possible that today's white LEDs are in fact more efficient than today's green LEDs. I don't know this to be the case, but it is possible, and I hope third time around my point is getting across: theoretically, green LEDs are more efficient, but today's advanced white LEDs are getting so efficient, they are surpassing the practical efficiency of actual colored LEDs, not theoretical ones.
