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Randomized Controlled Trial
. 2017 Aug 1;177:221-229.
doi: 10.1016/j.physbeh.2017.05.002. Epub 2017 May 1.

The Effects of Spectral Tuning of Evening Ambient Light on Melatonin Suppression, Alertness and Sleep

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Randomized Controlled Trial

The Effects of Spectral Tuning of Evening Ambient Light on Melatonin Suppression, Alertness and Sleep

Shadab A Rahman et al. Physiol Behav. .
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Abstract

We compared the effects of bedroom-intensity light from a standard fluorescent and a blue- (i.e., short-wavelength) depleted LED source on melatonin suppression, alertness, and sleep. Sixteen healthy participants (8 females) completed a 4-day inpatient study. Participants were exposed to blue-depleted circadian-sensitive (C-LED) light and a standard fluorescent light (FL, 4100K) of equal illuminance (50lx) for 8h prior to a fixed bedtime on two separate days in a within-subject, randomized, cross-over design. Each light exposure day was preceded by a dim light (<3lx) control at the same time 24h earlier. Compared to the FL condition, control-adjusted melatonin suppression was significantly reduced. Although subjective sleepiness was not different between the two light conditions, auditory reaction times were significantly slower under C-LED conditions compared to FL 30min prior to bedtime. EEG-based correlates of alertness corroborated the reduced alertness under C-LED conditions as shown by significantly increased EEG spectral power in the delta-theta (0.5-8.0Hz) bands under C-LED as compared to FL exposure. There was no significant difference in total sleep time (TST), sleep efficiency (SE%), and slow-wave activity (SWA) between the two conditions. Unlike melatonin suppression and alertness, a significant order effect was observed on all three sleep variables, however. Individuals who received C-LED first and then FL had increased TST, SE% and SWA averaged across both nights compared to individuals who received FL first and then C-LED. These data show that the spectral characteristics of light can be fine-tuned to attenuate non-visual responses to light in humans.

Keywords: Alertness; Circadian; Light; Melatonin; Sleep; Spectrum.

Figures

Figure 1
Figure 1. Study protocol, spectral characteristics of experimental lighting and representative melatonin profiles
Representative study raster of a participant maintaining a sleep schedule from midnight to 0800 h (A). White bars represent awake under ambient ~90 lux fluorescent light; gray bars represent awake under ambient dim (<3 lux) light; black bars represent sleep in darkness; white hashed bars represent experimental light exposure. Spectral irradiance profile of the FL (gray line) and C-LED (black line) sources (B). Data were collected in 4 nm bins and are expressed as averages in 24 nm bins for the C-LED. Representative 14 h melatonin profiles are shown from participants 3205V (C) and 3408V (D) across the four consecutive study days. Shaded areas show the area under the curve. For each condition, the time (EST) at which the melatonin profile crossed the DLMO threshold is reported (hh:mm) and marked as X.
Figure 2
Figure 2. Effects of spectral tuning on pre-bed melatonin suppression
Melatonin secretion related outcome measures included the time course of melatonin secretion profiles during the 6-h constant posture interval under C-LED (black line), FL (gray line) and dim light (gray dashed line) (A), melatonin area under the curve (AUC) secretion during the 6-h CP under C-LED and FL conditions (B), and melatonin suppression calculated as the difference in the AUC during the 6-h CP interval of the light exposure adjusted to the corresponding dim-light control interval 24 h earlier (C). Data are expressed as group means ± SEM. * p<0.05; between lighting conditions.
Figure 3
Figure 3. Effects of spectral tuning on pre-bed alertness and sleep
Pre-bedtime alertness was assessed using subjective sleepiness (A), reaction time on a 10-min psychomotor vigilance task (B), and EEG spectral profiles from Fz- (C), Cz- (D), Pz- (E) and Oz- (F) derivations. Sleep related outcome measures were assessed based on the lighting condition (C-LED vs. FL; G, H, I, J) and based on the order of presentation of the lighting condition (C-LED/FL vs. FL/C-LED; K, L, M, N). Sleep related outcome measures included total sleep time (G, K), % sleep efficiency [(TST/TIB)*100] (H, L), and slow wave activity during the first 90-min of non-rapid eye movement sleep calculated from the C3- (I, M) and C4- (J, N) derivations. Data are expressed as group means ± SEM. * and ● p<0.05 between lighting conditions.

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