Determination of lights that are isoluminant for both scotopic and photopic vision

A set of lights can be defined as D isoluminant if it is simultaneously isoluminant for both photopic and scotopic vision. Methods for determining sets of D-isoluminant lights are provided. It is shown that monochromatic lights cannot be made D isoluminant with one another for most of the spectrum and that particular white lights can each be made D isoluminant with a particular monochromatic light. Rules are provided for determining D isoluminance in dichromatic and trichromatic mixtures. The potential uses and limitations of D-isoluminant stimuli are discussed.