I found it here: Luminous efficacy - Wikipedia, the free encyclopedia.
I and some other are researching about different light sources, environmental inpact, efficacy, etc. We are gonna answer what the maximum efficacy messured in lm/W is for a light source emitting white light. A light wave with wavelength 555 nm has the maximum efficacy and it is 683 lm/W, but white light must consist of more than one wavelength, at least two different (I suppose), and hence cannot retain that efficacy. I guess we are gonna answer what the maximum theoretically efficacy. The tricky thing is just finding the optimal combination of three light waves (I guess) which results in white light and together have the maximum luminous efficacy... Can someone help me and my group here? ^^;;
But before we can answer that we must answer what white light is according to C.I.E., I have looked at wikipedia and searched the web with google to find the definition of white light, but I haven't found very much, at least not the definition. Does anyone know what C.I.E. means white light is?