The Hue (or simply, the "colour") is the dominant Wavelength or
dominant frequency
Energy distribution of a light source with a dominant frequency near the red
end of the frequency range
The integration of the energy for all the visible wavelengths is proportional
to the intensity of the colour
Intensity : Radiant Energy emitted per unit of time, per unit solid angle,
and per unit projected area of the source (related to the luminance of the
source)