I recall that in college ('68-'72) a standard joke when someone asked "What's new?" was to answer "E/h" (since E = h nu describes Planck's constant h (I think) ... where nu is the frequency of a photon. If so, I'd guess that for an arbitrary (constant) frequency nu (OK, gamma), V(gamma) just needs to be multiplied by the ratio gamma / (540*10^12 Hz), or in other words for any frequencies gamma_1, gamma_2: V(gamma_1) / V(gamma_2) = gamma_1 / gamma_2. (If this is dumb, sorry about that.) —Dan Adam Goucher wrote: ----- ... "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? -----