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

Abstract

ObjectivesArtificial 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.MethodsWe 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.ResultsOur 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.ConclusionsOur 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.

Light Modulation of Human Clocks, Wake, and Sleep

“…More recently, it was also demonstrated in humans that filtering shorter wavelengths of light [65] or using orange/red light exposure [54,66] in the evening increased sleep duration [54,65], sleep propensity [66], without suppressing melatonin [54,65], as shown by several studies in humans including those with new approaches of spectral tuning [58] and metameric light [101]. The exact sleep-promoting mechanisms of longer wavelength light exposure in the evening still need to be elucidated.…”

Pupil responses to hidden photoreceptor–specific modulations in movies

“…Commercially available VDUs have three primaries, which reflects the fact that human colour vision in photopic light levels is trichromatic. However, this study and a recent one [17] employing a similar system find that non-visual responses can be manipulated with a modified VDU with more than three primaries. Additionally, there is more and more evidence that melanopsin contributes to “classical” visual functions such as the perception of brightness [22, 37], colour [9, 38], space (humans: [9]; mice: [39]), and other visual attributes (humans: [24], mice: [40–42]).…”

Visual and non-visual properties of filters manipulating short-wavelength light

“…This is consistent with the view that melanopsin activation, which significantly drives steady-state pupil size in humans 65,66 , is severely reduced under short-wavelength filters. Under most real-world conditions, the correlation between luminance and melanopsin activation is probably well-constrained, except with chromatic filters and experimental conditions in which the decoupling can be lead to up to a three-fold difference in melanopsin activation with no or little nominal difference in luminance 67,68 . Importantly, optical quality of the retinal image depends on pupil size 69 , which needs to be factored into filter assessments.…”