spectral luminous efficiency n (General Physics) a measure of the efficiency of radiation of a given wavelength in producing a visual sensation. It is equal to the ratio of the radiant flux at a standard wavelength to that at the given wavelength when the standard wavelength is chosen so that the maximum value of this ratio is unity. Symbol: V(?) (for photopic vision) or V?(?) (for scotopic vision) Collins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014