While “circadian lighting” varies in definition, it generally refers to design that uses intensity and spectrum of light for a non-visual effect—namely, to support regulation of circadian rhythms. A new study suggests that by enabling intensity and spectral adjustment and optimizing exposure based on time of day, designers and owners can minimize the energy tradeoff imposed by associated typically much-higher light levels. This would entail use of an advanced lighting control system capable of scheduled dimming and perhaps spectral emission adjustment.