Identification of the blue-yellow metameric locus of the circadian stimulus model

Circadian lighting models are used to predict the effects of light stimuli on human circadian rhythms. These effects are typically quantified by the expected magnitude of nocturnal melatonin suppression in humans. Most circadian lighting models are based on continuous action spectra and as a result, small changes in spectral content of light stimuli do not result in significant changes in predicted circadian effects. One circadian lighting model, the so-called circadian stimulus (CS) model is notable for its incorporation of a blue-yellow opponency function that inherently results in a discontinuous action spectrum. This means that according to the CS model the predicted circadian impact of lighting can vary significantly depending on whether a spectrum is blue-dominated or yellow-dominated. The locus of metameric blue-dominated and yellow-dominated spectra has never been clearly identified despite the importance of this knowledge to lighting designers attempting to us the CS model in order to achieve desired circadian effective lighting scenarios. The present study uses a Monte Carlo simulation based on measured spectral power distributions to identify the chromaticity locus associated with both blue-dominated and yellow-dominated spectra according to the CS model.