Effects of Different Colors of Light on Human Physiology
Condition: Healthy; Circadian Rhythm
Study type: Interventional

Summary: 
      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.
    

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.
    

Intervention name(s): Monochromatic visible light exposure
Intervention type(s): Device
Intervention description(s): Monochromatic light in the visible range from 420-620 nm up to 60uW/cm2 for 6.5 hours
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: light; wavelength; action spectrum; circadian; melatonin; alertness; performance; arousal