Standardized and calibrated light stimuli via head-mounted displays for investigating the non-visual effects of light

Light influences human physiology profoundly, affecting the circadian clock and suppressing the endogenous hormone melatonin. Experimental studies often employ either homogenous full-field stimulation, or overhead illumination, which are hard to standardize across studies and laboratories. Here, we present a novel technique to examine non-visual responses to light using virtual-reality (VR) head-mounted displays (HMDs) for delivering standardized and calibrated light stimuli to observers in a reproducible and controlled fashion. We find that VR HMDs are well-suited for delivering standardized stimuli defined in luminance and across time, with excellent properties up to 20 Hz. We examine melatonin suppression to continuous luminance-defined light stimuli in a sample of healthy participants (n=31, mean±SD age: 27.4±5.6), and find robust melatonin suppression in 27 out of 31 participants (87% of the sample). Our findings demonstrate that VR HMDs are well-suited for studying the mechanisms underlying human non-visual photoreception in a reproducible and standardized fashion.