Predicting Human Nocturnal Nonvisual Responses to Monochromatic and Polychromatic Light With a Melanopsin Photosensitivity Function

Abstract

The short-wavelength (blue) light sensitivity of human non-visual responses is recognised as being melanopsin-based. However, whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving non-visual responses remains to be established. Monochromatic (λ max 437, 479 and 532 nm) and polychromatic (colour temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time and subjective alertness and mood was assessed.Young, healthy male participants aged 18 -35 years (23.6 ± 3.6 yrs; mean ± SD; n = 12) participated in 12 overnight sessions that included an individually timed 30 min light stimulus on the rising limb of the melatonin profile. At regular intervals before, during and after the light stimulus subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels and an auditory reaction time task (psychomotor vigilance task: PVT) was performed. Proc GLM repeated measures ANOVA analysis revealed that significantly lower melatonin suppression was observed with the polychromatic light conditions (4000 K and 17000 K) compared to the 'melanopsin photonmatched' monochromatic light conditions (p < 0.05). In contrast, whilst subjective alertness significantly increased across the course of the light exposure it was significantly lower under the 479 nm monochromatic light condition compared to the 437 and 532 nm monochromatic and both polychromatic light conditions. The demonstration that the melatonin suppression response to polychromatic light was significantly lower than predicted by the melanopsin photosensitivity function suggests that this function is not the sole consideration when trying to predict the efficacy of broadband lighting. The different spectral sensitivity of the subjective alertness and melatonin suppression responses may imply a differential involvement of the cone photopigments. An analysis of the photon densities in specific wavelength bands for the polychromatic lights used in this and our previous study suggests that the spectral composition of a polychromatic light source, and particularly the very short wavelength content, may be critical in determining response magnitude for the non-visual effects of nocturnal light.4

Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness

“…Suppression of melatonin by exposure to evening light may be an underlying mechanism by which light acutely increases alertness, as seen in the present study and in previous reports (14)(15)(16)(17)(18)(19). Other studies, however, have not found a relationship between alertness and melatonin levels during light exposure (20,21) or have shown changes in alertness induced by light exposure during the day, when melatonin levels are at low or undetectable levels (22)(23)(24).…”

Effect of simultaneous exposure to extremely short pulses of blue and green light on human pupillary constriction

“…Thus, a b/y pathway originates in the small bistratified RGCs and associated interneurons that combine excitation from S-cones and inhibition from (L + M)-cones [39]. Therefore, the responses of ipRGCs activated by S-cones might be reduced by inhibition from (L + M)-cones on simultaneous exposure to blue and green light, and NIF functions might show subadditivity to some types of polychromatic light [32–34] and two simultaneous exposures to monochromatic light [29], as in the present study.…”

“…This effect is called the subadditive response to light [29]. Figueiro et al [32, 33] and Revell et al [34] also identified the subadditive effects of monochromatic and polychromatic light on melatonin suppression, suggesting that cones affected the ipRGC response. However, it remains unclear whether the subadditive response affects pupillary constriction.…”

Chromatic clocks: Color opponency in non-image-forming visual function

“…It should be noted, however, that a more recent study of melatonin suppression using monochromatic lights with matched photon density found a peak at 480 nm (Najjar et al, 2014), suggesting that melanopsin makes the dominant contribution. Nonetheless, two studies investigating melatonin suppression by exposure to different polychromatic light sources have provided evidence for sub-additive responses that could be indicative of cone-opponent inputs (Figueiro et al, 2004; Revell et al, 2010), although a follow up study by the authors of one of those papers failed to find an opponent effect of combining short and long wavelength monochromatic stimuli (Papamichael et al, 2012). One model of the human circadian system explicitly includes an S-opponent input (Rea et al, 2010) but the evidence supporting such a role is far from conclusive.…”