Abstract
Light not only enables humans to see via the visual pathway originating in the retinal rods and cones, but also affects cognition, mood, hormone balance and biological rhythms, via the non-visual pathway originating in the intrinsically photosensitive melanopsin-containing retinal ganglion cells (ipRGCs). Through the use of spectrally tuneable multi-channel LED light sources, we are able to sculpt illumination spectra to modulate activity selectively in the visual and non-visual pathways, and thereby explore behavioral effects and interactions between the two. In visual experiments examining surface color perception, we find that thresholds for visually discriminating illumination changes are highest for blueish daylight illuminations – i.e. color constancy is best for naturally encountered illuminations. In other behavioral experiments, we find a trade-off in the effects of photopic (visual) and melanopic (non-visual) irradiance: lights of the same melanopic irradiance but very different photopic irradiance are equally effective in suppressing melatonin levels and sleepiness at night, but reduce performance on visual attention tasks and worsen mood, relative to lights of low melanopic irradiance and high photopic irradiance. These and other results may help guide the use of tuneable illumination in the home and workplace to optimise individual performance, dependent on task needs, circadian phase and the environment.