There seems to be a lot of recent excitement about the redefinition of the kilogram, but I'm more worried about the candela. On the face of it, it seems to have a relatively simple definition: "The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540*10^12 Hz and that has a radiant intensity in that direction of 1/683 watt per steradian." where luminous intensity is defined as: I_v = 683 V(gamma) I_e where I_e is the radiant intensity (in watts per steradian) and V(gamma) is the 'standard luminosity function' (which must be equal to exactly 1 when gamma = 540*10^12 Hz, for these definitions to be consistent). But this raises the question: what is V(gamma) in general? I've found a tabulation of values for integer * 10^-9 metre wavelengths in the visible interval: http://donklipstein.com/photopic.html but no indication as to how to compute V(gamma) for any of the 2^(aleph_null) other wavelengths beside the 401 provided. Any ideas? Best wishes, Adam P. Goucher