I will take a stab at this one for you.
Expressed in Lumens, it is the time rate of the flow of Light.
Radiant energy in the visible region of the spectrum, varies in its ability to produce visual sensation; the variation depending on the wavelength.
Simply, some colors appear "brighter" than others.
The ratio of the luminous flux to the corresponding radiant flux is the Luminosity Factor, or Visibility Factor - and is expressed in Lumens Per Watt.
This varies with wavelength, having a maximum at approximately 5,550 Angstroms.
In a nutshell, the topic is referring to the color tones which comprise White Light - either as individual, stand-alone colors, as "mixed" combinations of colors, or all colors combined - as in White Light.
Sound kind of right? Also, does this make sense and/or appear to be what you are looking for as a description?
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!