Some thoughts on the practical limits of LED efficiency

[Canuke]

By the laws of physics, the only way we can make a 100% efficient white emitter is to mix light from 100% efficient red, green, and blue emitters (or perhaps even four or five emitters for greater color rendering).

Actually, for the most daylight-like color rendering you would need not only additonal emitters to fill in the spectral gaps an RGB setup would have (probably add a yellow-green emitter at 555 nm and a cyan one at 500nm) but you'd also have to add in some NUV so that certain fluorescent colors look right.