Blue-Enriched Morning Light as a Countermeasure to Light at the Wrong Time: Effects on Cognition, Sleepiness, Sleep, and Circadian Phase

Abstract

Light during the day and darkness at night are crucial factors for proper entrainment of the human circadian system to the solar 24-h day. However, modern life and work styles have led to much more time spent indoors, often with lower daytime and higher evening/nighttime light intensity from electrical lighting than outdoors. Whether this has long-term consequences for human health is being currently investigated. We tested if bright blue-enriched morning light over several days could counteract the detrimental effects of inadequate daytime and evening lighting. In a seminaturalistic, within-between subject study design, 18 young participants were exposed to different lighting conditions on 3 evenings (blue-enriched, bright orange, or dim light), after exposure to 2 lighting conditions (mixed blue-enriched light and control light, for 3 days each) in the mornings. Subjective sleepiness, reaction times, salivary melatonin concentrations, and nighttime sleep were assessed. Exposure to the blue-enriched morning lighting showed acute wake-promoting effects and faster reaction times than with control lighting. Some of these effects persisted until the evening, and performance improved over several days. The magnitude of circadian phase shifts induced by combinations of 3 different evening and 2 morning lighting conditions were significantly smaller with the blue-enriched morning light. During the night, participants had longer total sleep times after orange light exposure than after blue light exposure in the evening. Our results indicate that bright blue-enriched morning light stabilizes circadian phase, and it could be an effective counterstrategy for poor lighting during the day and also light exposure at the wrong time, such as in the late evening.

Light Modulation of Human Clocks, Wake, and Sleep

“…Effects of prior light history Influence of light history on non-visual responses (Hébert et al [49]; Smith et al [50]; Jasser et al [51]; Chang et al [52]; Chellappa et al [53]; Münch et al [54])…”

“…Impact of light on sleep (i) Impact of brighter light during daytime increases SWS accumulation during the following night (Wams et al [59]; Nowozin et al [60]) (ii) Effects of short-wavelength light, including from LED devices, before bedtime on sleepiness (e.g., van der Lely et al [61]), sleep onset (e.g., Chang et al [62]), REM sleep, SWS and sleep architecture (Münch et al [63]; Chellappa et al [64]) (iii) Impact of longer wavelengths light prior to sleep on sleep promotion (Münch et al [54]; Ostrin et al [65]; van der Meijden et al [66]) (iv) Impact of light during sleep on melatonin suppression (Obayashi et al [67]; Zeitzer et al [68]) and SWS (Cho et al [ The melatonin secretion pattern, considered as one of the best indirect markers of the circadian clock in the SCN [70], has an action spectrum for its suppression by light that peaks at~480 nm ( Figure 1) [27][28][29], which is the same as that of ipRGCs sensitivity [71,72]. Phase-shifting responses mediated by the master circadian clock are also more sensitive to short wavelengths of 460-470 nm when compared to medium wavelengths of light at 555 nm [30] or long wavelength light at 600 nm [31].…”

“…Furthermore, prior illuminance history has also been shown to influence the magnitude of the direct alerting effect of a light stimulus [26]. Importantly, recent findings suggest that prior light exposure can also reduce the subsequent responsivity of the circadian clock, such that bright blue-enriched polychromatic light exposure in the morning, as compared to a control lighting, reduced phase shifts in response to light exposures in the evening [54].…”

“…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.…”

Optimising sleep for night shifts

“…One approach to repaying the sleep debt is to take a nap of 90 minutes or 180 minutes (one or two full sleep cycles), and then to realign with daytime sleep cues by going outside into the bright light, socialising, and aiming for bed as near to the usual time as possible, but further work is required to establish whether such an approach is beneficial 293341. A meta-analysis of 66 studies concluded that regular exercise leads to improvement in sleep quantity and quality,42 but the optimum timing, duration, and type of exercise for sleep promotion have yet to be determined.…”