Effects of Different Colors of Light on Human Physiology

Mechanism Underlying the Effects of Blue Light in Humans

This study will determine which color of light is most effective in stimulating a range of biological functions in humans including activation of sleep-wake regulatory system (alertness, performance, microsleeps, brain activity), activation of the nervous system (heart rate, temperature, blood pressure, breathing rate), and shifting the timing of the internal 24-hour (circadian) pacemaker.

Study Overview

• Status: Completed
• Conditions: Healthy; Circadian Rhythm
• Intervention / Treatment: Device: Monochromatic visible light exposure

Detailed Description

Light has long been proposed to have a stimulatory effect on a range of biological functions in humans including increased feelings of activation, such as improved alertness or ability to perform. The mechanisms underlying how light stimulates these neurobiological systems remain to be elucidated. We propose to investigate the effects of different colors of light on human physiology, and in particular, test the claims that specific colors of light preferentially stimulate neurobiological, physiological and hormonal systems. Using classical photobiological techniques, we will construct action spectra for the effects of different colors of light on a range of non-image forming responses in humans.

We will test the hypotheses that: 1) light-induced activation of the neurobiological sleep-wake regulatory system, as indicated by increased alertness, faster reaction time, suppression of EEG alpha activity, microsleeps and slow rolling eye movements, and suppression of pineal melatonin, is most sensitive to retinal exposure to short wavelength blue light (460 nm) compared to equal photons of other colors of visible light; 2) light-induced activation of autonomic and hypothalamic-pituitary-adrenal axis measures of arousal, as indicated by increased heart rate variability, core body temperature, blood pressure, respiration rate, plasma cortisol levels and urinary catecholamines, is most sensitive to exposure to short wavelength blue light (460 nm) compared to equal photons of other colors; 3) phase shifts of the human circadian pacemaker, as assessed by changes in temperature, melatonin and cortisol rhythms, are most sensitive to exposure to short wavelength blue light (460 nm) compared to equal photons of other colors. The resultant action spectra will help to identify the photoreceptor mechanism(s) by which light activates arousal and circadian resetting, these non-image-forming physiological responses and enable us to distinguish between major candidate photoreceptive mechanisms, including potential novel photoreceptor systems, that might mediate such responses.

• Study Type: Interventional
• Enrollment (Actual): 47
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Massachusetts
    • Boston, Massachusetts, United States, 02115
      • Division of Sleep Medicine, Brigham and Women's Hospital

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 30 years (Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• Free from any acute, chronic or debilitating medical, psychological, or ophthalmological conditions
• Drug-free (including caffeine, nicotine, and alcohol) for entire study duration

Exclusion Criteria:

• History of drug or alcohol dependency
• History of psychiatric illnesses or evidence of psychopathology according to standardized questionnaires, or in a structured clinical interview
• Night shift work during the past 3 years
• Transmeridian travel in the last 3 months

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

6

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: 1; 420 nm light	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Experimental: 2; 480 nm	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Experimental: 3; 507 nm	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Experimental: 4; 555 nm	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Experimental: 5; 620 nm	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Experimental: 6; 460 nm	Device: Monochromatic visible light exposure; Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Subjective alertness prior to, during and after light exposure	9.5 hours
Auditory psychomotor performance prior to, during and after light exposure	9.5 hours
EEG power frequency prior to, during and after light exposure	9.5 hours
Plasma melatonin and cortisol prior to, during and after light exposure	60 hours
Heart rate, blood pressure, respiration rate and temperature prior to, during and after light exposure	9.5 hours
Urinary catecholamines prior to, during and after light exposure	32 hours

Collaborators and Investigators

• Sponsor: Brigham and Women's Hospital
• Collaborators: National Center for Complementary and Integrative Health (NCCIH)
• Investigators: Principal Investigator: Steven W Lockley, Ph.D., Brigham and Women's Hospital, Harvard Medical School

Publications and helpful links

General Publications

• Gooley JJ, Chamberlain K, Smith KA, Khalsa SB, Rajaratnam SM, Van Reen E, Zeitzer JM, Czeisler CA, Lockley SW. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab. 2011 Mar;96(3):E463-72. doi: 10.1210/jc.2010-2098. Epub 2010 Dec 30.

Study record dates

Study Major Dates

• Study Start: April 1, 2005
• Primary Completion (Actual): February 1, 2007
• Study Completion (Actual): February 1, 2007

Study Registration Dates

• First Submitted: September 12, 2005
• First Submitted That Met QC Criteria: September 13, 2005
• First Posted (Estimate): September 20, 2005

Study Record Updates

• Last Update Posted (Estimate): August 12, 2014
• Last Update Submitted That Met QC Criteria: August 8, 2014
• Last Verified: August 1, 2014

More Information

Terms related to this study

• Keywords: melatonin; circadian; performance; light; arousal; alertness; wavelength; action spectrum
• Other Study ID Numbers: R01AT002129-01 (U.S. NIH Grant/Contract)