Objective: At the beginning of this century, a novel photopigment, melanopsin, was discovered in a
sub-class of retinal ganglion cells and its action spectrum was described. Shortly after, it became evident that
melanopsin is a major contributor to non-visual eye-mediated effects of light on e.g. the circadian, neuroendocrine
and neurobehavioral systems. First applied studies pointed out that these non-visual effects of light are
relevant for wellbeing, performance and general health. A standardized measurement metric for these nonvisual
effects does not exist, but would ease application. Such a metric termed as ‘melanopic lux’ has been
recently introduced and was shown to be superior to describe non-visual effects in animal studies compared to
Methods: We aimed at showing some validity of melanopic lux in humans using a seminaturalistic setting.
Therefore, we analyzed the impact of different lighting conditions on melatonin suppression and subjective
sleepiness by calculating effective illuminance based on single photopigment sensitivities. We retrospectively
analyzed data from our laboratory, where young participants were exposed to a total of 19 different polychromatic
lighting conditions, for 30 minutes in the evening, one hour prior to habitual bedtime. Saliva samples for
melatonin concentration measures and subjective sleepiness were regularly assessed. The photopic illuminance
of all lighting conditions ranged from 3 to 604 lx. Stepwise for- and backward regression analyses showed that
melanopic lux was the best predictor for changes in melatonin concentrations (but not subjective sleepiness);
R²=0.16 (p<0.05). In addition, we found a significant dose-response relationship between melanopic lux and
changes in melatonin concentrations for 18 different lighting conditions (adjusted R²=0.52; p=0.004), similarly
to what was previously reported for photopic lux.
Results: Our results indicate some new relevance for the application of melanopic lux as an additional metric
to predict non-visual light effects of electrical light sources for nursing homes, work places, and homes.