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Cited by 101Circadian rhythm and melatoninSleep and Work-Related FatigueSleep and related disorders

Phase Delaying the Human Circadian Clock with Blue-Enriched Polychromatic Light

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Smith, Mark R., Eastman, Charmane I.·2009·Chronobiology International
DOI 10.1080/07420520902927742PMC PMC2828683
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Abstract

The human circadian system is maximally sensitive to short-wavelength (blue) light. In a previous study we found no difference between the magnitude of phase advances produced by bright white versus bright blue-enriched light using light boxes in a practical protocol that could be used in the real world. Since the spectral sensitivity of the circadian system may vary with a circadian rhythm, we tested whether the results of our recent phase-advancing study hold true for phase delays. In a within-subjects counterbalanced design, this study tested whether bright blue-enriched polychromatic light (17000 K, 4000 lux) could produce larger phase delays than bright white light (4100 K, 5000 lux) of equal photon density (4.2x10(15) photons/cm(2)/sec). Healthy young subjects (n = 13) received a 2 h phase delaying light pulse before bedtime combined with a gradually delaying sleep/dark schedule on each of 4 consecutive treatment days. On the first treatment day the light pulse began 3 h after the dim light melatonin onset (DLMO). An 8 h sleep episode began at the end of the light pulse. Light treatment and the sleep schedule were delayed 2 h on each subsequent treatment day. A circadian phase assessment was conducted before and after the series of light treatment days to determine the time of the DLMO and DLMOff. Phase delays in the blue-enriched and white conditions were not significantly different (DLMO: -4.45+/-2.02 versus -4.48+/-1.97 h; DLMOff: -3.90+/-1.97 versus -4.35+/-2.39 h, respectively). These results indicate that at light levels commonly used for circadian phase shifting, blue-enriched polychromatic light is no more effective than the white polychromatic lamps of a lower correlated color temperature (CCT) for phase delaying the circadian clock.

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  • Studies by Smith et al. demonstrated that blue-enriched white light (17 000 °K) does not outperform standard white light (4100 °K) in phase-advancing or phase-delaying effects.

    “Studies by Smith et al. [32,33], have demonstrated that, in a similar way, frequently used bright-light therapy photon densities (4.2 vs. 4.9 10E15 photons/cm2/s), blue-enriched white light (17 000 °K) does not outperform standard white light (4100 °K) in phase-advancing or phase-delaying effects.”

    From Low-intensity blue-enriched white light (750 lux) and standard bright light (10 000 lux) are equally effective in treating SAD. A randomized controlled study (2011) · cites this paper as [32]

    The Abstract reports no significant difference between phase delays under 17,000 K blue-enriched and 4,100 K white light, and says a previous study found no difference in phase advances. However, the Methods (Bright-Light Treatment; page unavailable) state that both conditions in this study delivered 4.2 × 10¹⁵ photons/cm²/s; this paper does not establish the cited 4.9 × 10¹⁵ figure. (LLM, conf=0.86)

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  • Low levels of illumination are sufficient to trigger awakening and the effect on circadian rhythm gets saturated at high illumination levels.

    “Studies indicate that low levels of illumination are sufficient to trigger awakening and there are hints that the effect on circadian rhythm gets saturated at high illumination levels 38, 39.”

    From The inner clock-Blue light sets the human rhythm (2019) · cites this paper as [39]

    The Discussion (page not provided) reports evidence that circadian phase shifts may saturate at higher illumination, while noting that the saturation level under real-world lighting conditions is unknown. It also describes dim blue light producing phase shifts, but does not say that low illumination triggers awakening; the light treatment described as occurring ‘upon awakening’ began after waking. (LLM, conf=0.88)

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Authors
Smith, M. R., & Eastman, C. I.
Affiliations
Rush University Medical Center (US)
Corresponding author
Eastman, Charmane I.
ORCID
Eastman, Charmane I.
Venue
Chronobiology International
Publisher
Informa UK Limited
Published
2009-01
Volume
26
Issue
4
Pages
709-725
ISSN
  • 0742-0528 (ISSN-L)
  • 1525-6073
DOI
10.1080/07420520902927742
PMC
PMC2828683
OpenAlex
W2029209620
Cited by
100
References
77
Citations by year
2026: 2 · 2025: 1 · 2024: 3 · 2023: 5 · 2022: 4 · 2021: 4 · 2020: 5 · 2019: 2 · 2018: 6 · 2017: 4 · 2016: 5 · 2015: 7 · 2014: 4 · 2013: 5 · 2012: 12
FWCI
6.43
Type
journal article
Language
en
Open access
Locations
  • Chronobiology International (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
  • Rush University
  • National Institutes of Health
  • National Institute of Nursing Research (R01NR007677)
Topics
  • Life Sciences › Neuroscience › Endocrine and Autonomic Systems › Circadian rhythm and melatonin
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and Work-Related Fatigue
  • Social Sciences › Psychology › Experimental and Cognitive Psychology › Sleep and related disorders
Keywords
circadian phase delay, blue-enriched light, polychromatic light, white light, circadian phase shifting, dim light melatonin onset, correlated color temperature, circadian clock
MeSH terms
Adult, Circadian Rhythm, Darkness, Female, Humans, Light, Lighting, Male, Melatonin, Reaction Time, Sleep, Wakefulness, Patient Selection, Young Adult

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