For the standard conditions chosen in establishing this standard luminosity function (photopic vision[?]) the luminously effective radiant intensity in lumens of radiation of spectral intensity Jλ watts/unit wavelength is given by
where yλ is the standard lumiunosity function normalized to a value of unity at 555 nanometers (see luminous coefficient). The numerical values for yλ are commonly given as a luminosity curve[?].
For very low levels of intensity (scotopic vision[?]) the peak of the luminosity function curve shifts toward the violet for young eyes (507 mμ) with an absolute value of 1746 lumens/watt.
wikipedia.org dumped 2003-03-17 with terodump