Exploiting metamerism to regulate the impact of a visual display on alertness and melatonin suppression independent of visual appearance

Objectives
Artificial light sources such as visual display units (VDUs) elicit a range of subconscious and reflex light responses, including increases in alertness and suppression of pineal melatonin. Such responses employ dedicated retinal circuits encompassing melanopsin photoreceptors. Here, we aimed to determine whether this arrangement can be exploited to modulate the impact of VDUs on melatonin onset and alertness without altering visual appearance.

Methods
We generated a five-primary VDU capable of presenting metameric movies (matched for color and luminance) but varying in melanopic-irradiance. Healthy human participants (n = 11) were exposed to the VDU from 18:00 to 23:00 hours at high- or low-melanopic setting in a randomized cross-over design and measured salivary melatonin and self-reported sleepiness at 30-minute intervals.

Results
Our VDU presented a 3× adjustment in melanopic-irradiance for images matched photometrically for color and luminance. Participants reported no significant difference in visual appearance (color and glare) between conditions. During the time in which the VDU was viewed, self-reported sleepiness and salivary melatonin levels increased significantly, as would be expected in this phase of the diurnal cycle. The magnitude of the increase in both parameters was significantly enhanced when melanopic-irradiance was reduced.

Conclusions
Our data demonstrate that melatonin onset and self-reported sleepiness can be modulated independent of photometric parameters (color and luminance) under a commonly encountered light exposure scenario (evening use of a VDU). They provide the first demonstration that the impact of light on alertness and melatonin production can be controlled independently of visual experience, and establish a VDU capable of achieving this objective.