Table 1.
Selective overview of published studies and methodological parameters regarding the effect of light, most notably in the blue spectrum, and illumination intensity on circadian rhythms, alertness, and sleep. Most studies in humans included an initial ophthalmological examination and evaluation of chronotype, constant posture protocols in the laboratory and dark adaptation episodes under polychromatic dim light for 0.5 to 2 hours before treatment exposure. Irradiance unit summarizes information about photon density, irradiance, illuminance, and luminance. The properties timing and duration refer to start and length of the respective treatment exposure, not the whole experimental protocol
| Light parameter | |||||||
|---|---|---|---|---|---|---|---|
| Study | Methodology | Spectral composition | Unit | Duration | Timing | Subjects (mean age ± SD) | Results |
| Lockley et al 30 | BMA | 555 and 460 nm | 6 × 1013 photons cm−2 s−1 | 6.5 h | 9.25 h before waketime | 16 healthy, (23.3 ± 2.4) | 460 nm induced a 2‐fold greater circadian phase delay |
| McIntyre et al 37 | BMA | polychromatic | ‐ | 1 h | Midnight | 13 healthy, (25.1 ± 6.4) | 1000 lx intensity suppress melatonin to near daytime levels; 350 lx significantly suppress nocturnal melatonin levels. |
| Munch et al 43 | Sleep: PSG, 8 EEG, EOG, EMG, ECG | 550 nm, 460 nm, polychromatic | 460 nm: 12.1 μW cm−2, 550 nm: 10.05 μW cm−2 | 2 h | 9:30 PM | 8 healthy, male (24.6 ± 3) | Small wavelength‐dependent effects of light on sleep architecture and EEG. Most likely an acute alerting effect continuing into sleep and/or an immediate phase delay induced by blue light. |
| Herljevic et al 48 | BMA | 548 and 456 nm | 7000‐12 000 lx vs. 150 lx | 0.5 h | ˜3.5 h pre melatonin peak | 13 pre‐ and 21 post‐menopausal women | Reduced melatonin suppression in elderly subjects following exposure to blue light, likely due to age‐related changes in lens density. |
| Sletten et al 49 | Questionaires: Alertness, sleepiness, mood, BMA | 548 and 456 nm | 200‐400 lx | 2 h | 8.5 h after DLMO | 11 young (23.0 ± 2.9), 15 old (65.8y ± 5.0) men. | Subjective alterness, sleepiness and mood response to blue light diminished in elderly compared to young subjects. No age effect in green light exposure. |
| Cajochen et al 57 | KSQ, CBT and surface skin temperature, ECG, SMA | 550 nm, 460 nm, polychromatic | 2.8 × 1013 cm−2 s−1 | 2 h | 10 h after waketime | 10 healthy, male (25.9 ± 3.8) | Blue light exposure in the evening suppressed melatonin more than green light exposure, and effected increased alerting response, core body temperature and heart rate. |
| Czeisler et al 59 | Night shift work treatment; Sleep‐wake logs, ECG, CBT, Cognitive‐performance tasks | Polychromatic | 150 and 7000‐12 000 lx | 8 h | Midnight | 8 healthy, male, 22‐29 years | Maladaptation of the human circadian system to night work can be treated with scheduled exposure to bright light at night and darkness during the day. |
| Davidson et al 62 | Molecular rhythms, high‐resolution optical microscopy & bioluminescence of SCN | Polychromatic | 200‐400 lx | 6 h phase shift | mPer2LUC knock‐in mice | Differences in circadian shifting kinetics are apparent among subjects and among organs. | |
| Khalsa et al 63 | BMA | Polychromatic | fixed gaze ∼10000 lx; free gaze ~5000‐9000 lx | 6.7 h, alternating gaze | centered in 16 h wake episode | 21 healthy, entrained | Phase delays occur when light stimulus is centered prior to the core body temperature minimum (CBTM), phase advances occur when light stimulus is centered after the CBTM, no phase shift occurs at CBTM. |
| Cajochen et al 68 | SMA, KSQ, KDT, GO/NOGO task, cognitive performance | LED with twice more 464 nm emission | LED 0.241 Wsr−1 m−2; CCFL 0.099 W sr−1 m−2) | 5 h | 6 h before bed time | 13 male (23.8 ± 5.0) | Evening exposure to blue enriched LED screen resulted in attenuated salivary melatonin and sleepiness levels, accompanied with increase in cognitive performance. |
| Wahnschaffe et al 71 | Sleep log and actimetry; SMA, VAS | White, zero blue component, high intensity light | 130 and 500 lx | 0.5 h | 1 h before bedtime | 9 healthy, (26.3 ± 4.2) | Yellow light exposure did not alter the increase of melatonin in saliva. Lighting conditions including blue components reduced melatonin increase significantly. Subjective alertness was significantly increased after exposure to light which included blue spectral components. |
| Chang et al 73 | Blood plasma melatonin assay, PSG, KSQ, EEG | LE‐eBook: blue enriched; Print book: white light | 30 and 3 lx | 4 h | 6 pm | 12 healthy, (24.9 ± 2.9) | LE‐e‐book condition compared to print book: suppressed evening levels of melatonin, delayed melatonin onset, delay sleep onset, less rapid eye movement (REM) sleep. |
| Kozaki et al 74 | SMA at 1 am and 9 am | Polychromatic white & blue enriched light | 300 and 10 lx | 1.5 h | 1 am, 9 am | 12 healthy, male (21.9 ± 0.9) | Findings suggest that daytime blue light exposure has an acute preventive impact on light‐induced melatonin suppression. |
| Kervezee et al 98 | Night shift protocol: transcriptome assay | Polychromatic | mean 2.6 ± 0.4 lx (SD) | 8 h | 10 h phase shift | 8 healthy | Reduction of rhythmic transcripts in the night shift condition. Mainly due to dampened rhythms & lower amplitudes rather than to a complete loss of rhythmicity. |
Abbreviations: BMA, blood melatonin assay; CBT, continuous body core temperature; DMLO, dim light melatonin onset; ECG, electrocardiogram; EEG, electroencephalography; EMG, electromyogramm; EOG, electrooculography; KDT, Karolinska drowsiness test; KSQ, Karolinska sleep questionnaire; PSG, polysomnography; PVT, psychomotor vigilance task; SMA, saliva melatonin assay; VSA, visual analogue scale.