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Day Light & Dark Night - Light & Our Bodies 

Circadian Explained

​Disclaimer - Not intended for medical advice, consult your doctor.

Circadian System Explained - Learning Objectives

  • What is your Circadian Cycle?
  • What influences your Circadian Rhythm?
  • Why is it harmful to have an out of balance circadian system?
  • Day Light & Dark Night - what does this mean?
  • What does the Circadian System Control?
  • Do plants and animals have Circadian Systems?
  • Circadian research topics?
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The sun plays an important role in our wake and sleep cycles,
known as your Circadian Rhythm.

Circadian System

Our ancestors evolved under the natural cycles of day-light and dark -night. Light is energy that influences mind and body - many chemicals in our bodies are controlled by light. 

Premature babies thrive under simulated sunrise to sunset - where the light changes color throughout the day, and they have a dark night sleep. Studies have shown them growing at a rate 50% faster than those under constant bright illumination. [1]  This makes sense, since we grow and heal while we sleep, naturally in the dark.

Melatonin is produced at night to direct our bodies to sleep. Exposure to blue tinted light can delay sleep for as much as two hours.
Picture

This Biological Clock diagram represents the natural circadian rhythm of a human day and night.

"A circadian rhythm is any biological process that displays an endogenous, entrainable oscillation of about 24 hours. These 24-hour rhythms are driven by a circadian clock, and they have been widely observed in plants, animals, fungi, and cyanobacteria." [1]

2017 Nobel Prize for Circadian Rhythm Research

Picture

The circadian clock anticipates and adapts our physiology to the different phases of the day.  Our biological clock helps to regulate sleep patterns, feeding behavior, hormone release, blood pressure, and body temperature.

The Nobel Prize in Physiology or Medicine 2017, for their discoveries of molecular mechanisms controlling the circadian rhythm
Jeffrey C. Hall, Michael Rosbash, Michael W. Young [3]

Daytime to Nightime Circadian Body Changes
Daytime to Nightime Circadian Body Changes

Morning Dove - Day Lark - Night Owl and Night Shift Work

Morning Dove - Day Lark - Night Owl and Night Shift Work
When do you sleep?
Each of us has our own biological rhythm.
Lighting researchers are beginning to learn more about this in studying night shift workers where it seems Night Owls have a lower incidence of cancer related illness from night shift work.

Night Shift Work, Chronotype, Sleep Duration, And Prostate Cancer Risk: CAPLIFE Study  
www.ncbi.nlm.nih.gov/pmc/articles/PMC7503878/
Table 2 Associations between PCa and night shift work, chronotype, and sleep duration.
Chronotype c
   Morning  247 (60.2)283 (60.8)0.6221
   Neither   125 (30.5)130 (28.0)0.94 (0.69–1.28)
   Evening   34 (8.3)45 (9.7)1.18 (0.72–1.93)
   Missing   4 (1.0)7 (1.5)

Researchers have been studying the effects of night shift work on nurses for many years. Since nurses work in hospitals, are willing to participate in research studies, and have equipment for testing on site, they have been the subject of night shift work studies for many years.
"Working at night and exposure to light at night causes a disturbance of circadian rhythms." 
Night Shift Work - A Risk Factor for Breast Cancer
www.ncbi.nlm.nih.gov/pmc/articles/PMC7013618/

Lighting designers and architects are learning to modify the lighting for night shift workers to include warm red lighting at night in corridors and work stations. Additionally this lower brightness and warmer temperature lighting also helps patients sleep. For more information visit the Healthcare Lighting page.
Healthy Light and Healthy Darkness
Healthy Light and Healthy Darkness

Interview With Talieh Ghane: What Is Healthy Lighting?

"Healthy lighting goes hand in hand with healthy darkness. My best advice from what I learned in my research on light and health is that our biological system needs contrast. So it cares about the contrast between the light that you are exposed to during the day and the darkness that you are exposed to during the night.
​Healthy lighting goes hand in hand with healthy darkness. 
Dim the lights in your home as you get closer to bedtime. Two hours before bedtime, eliminate digital screens. And in the day, if you can spend even 15 minutes of your lunchtime outdoors, do it, be exposed to high-level light that can regulate your circadian system, so you can sleep much better at night and be more productive during the day." [4]

Circadian Brain

Picture

Brain Signals

The controller of our Circadian System producing Melatonin is the Pineal Gland, this part of the Endocrine System, sometimes referred to as the 'third eye' is located deep inside our brain, directly above the optic chiasm. . It receives signals though our eyes, collecting information about light intensity and color via the optic nerves.  "Suprachiasmatic nuclei (SCN), located in the hypothalamus above the optic chiasm."

Hormones - Melatonin and Serotonin, are created in our bodies to signal us to sleep and wake.

Cyto-architecture is a biology term used to describe the study of the arrangement of cells and how this affects the performance of each organ. Often referred to as study of the brain structure, 'cyto' means 'cells' and 'architecture' originates from Greek arkhitekton 'master builder.' Studying the architecture of the brain,  is analogous to the study of buildings, their manner of construction and the arrangement of their parts. As recently as 2002 scientists discovered photoreceptors called ganglion cells (RGC) in our eye's retina that respond to light and send signals to our circadian system.  Scientists continue to search for understanding of the brain circuits, receptors, and their functions. [5]

The photoreceptors and their respective peak sensitivity wavelengths are the L-cones (564nm), M-cones (533nm), rods (507nm), iPRGC (480nm) and S-cones (437nm).  [6]
Picture

Circadian Response Curve
Blue light will keep you awake.

Use amber or red night lights.
Circadian rhythm sleep disorders, such as jet lag syndrome and shift work sleep disorder, are those specifically attributed to dysfunctions or insufficiencies in the circadian system. Taking into consideration the preeminence of the circadian clock in timing sleep, it is likely that other sleep disorders, such as insomnia, are also linked to circadian system abnormalities. [7]

Light Research Center - Lighting for Healthy Living - May 26, 2020

New website for lighting designers and others wanting to further understand the human circadian system and how to adjust lighting for healthy living.  ​https://www.lrc.rpi.edu/healthyliving/
LRC - Lighting for Healthy Living Website Launched - May 26, 2020
LRC - Lighting for Healthy Living Website Launched - May 26, 2020

Quantifying Circadian Light and Its Impact

February 13, 2017 article featured in Architectural Lighting Magazine
http://www.archlighting.com/technology/quantifying-circadian-light-and-its-impact_o
Melanopic lux is the wrong metric for describing circadian-effective light. Here is a better alternative. By Mariana Figueiro, Mark Rea 
  • Mariana Figueiro, FIES, is a professor at the Lighting Research Center at Rensselaer Polytechnic Institute, where she also directs the Light and Health program.
  • Mark Rea, FSLL, is a professor at the Lighting Research Center and has served as its director since its founding in 1988.
Blue Light Dimming cell phone and computer apps are available to shift computers and cell phones to dimmer warmer light after dark. Twilight is one example.

Footnotes

  1. Mark Rea, Director of the Lighting Research Center (LRC) and Professor of Architecture and Cognitive Sciences at Rensselaer Polytechnic Institute. Presentation Lightfair 2006 Current standards described in Lighting for Today's Neonatal Intensive Care Unit. 2010 http://www.sciencedirect.com/science/article/pii/S1527336910000322
  2. Circadian Rhythms in Humans, Animals, & Plants. https://islandpress.org/book/ecological-consequences-of-artificial-night-lighting?utm_source=Light+Pollution+and+islandpress.org/book/ecological-consequences-of-artificial-night-lighting?utm_source=Light+Pollution+and+the+Ecological+Consequences+of+Artificial+Night&
  3. "The 2017 Nobel Prize in Physiology or Medicine - Press Release". Nobelprize.org. Nobel Media AB 2014. Web. 14 Nov 2017. <http://www.nobelprize.org/nobel_prizes/medicine/laureates/2017/press.html>
  4. https://www.alconlighting.com/blog/learning-lab/talieh-ghane-what-is-healthy-lighting/
  5. Brown University, Department of Neuroscience    https://neuroscience.brown.edu/Berson/research.html
  6. ​https://www.alconlighting.com/blog/learning-
  7. ...study ... Spectral Power Densities (SPDs) matching the various human photoreceptors’ peak-sensitivity wavelengths.​https://www.researchgate.net/project/Anatomy-of-Light
  8. The human circadian system in normal and disordered sleep.  http://www.ncbi.nlm.nih.gov/pubmed/16336035

Photo Credits

  • Human Biological Clock - Wiki Circadian Brain - CTC - http://braintreatmentcenter.com/
  • Circadian Clock© The Nobel Committee for Physiology or Medicine. Illustrator: Mattias Karlén.
  • Daytime to Nightime Circadian Body Changes - https://www.alconlighting.com/blog/lighting-design/effects-of-light-color-intensity-mind-body/
  • How Blue Light affects your circadian rhythm. - Alcon Lighting - ​https://www.alconlighting.com/blog/learning-lab/talieh-ghane-what-is-healthy-lighting/
Picture

Related Topics

Light Therapy, Nightlights, Sleep, Blue Dimming Apps, Ecology of Night Lighting, Dark Sky

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  • Home
  • Color & Perception
    • CHROMA Topics
    • Color Spectrum - Light is Energy
    • Color in Light
    • Color in Nature
    • Color in Paint
    • Why does paint fade?
    • Color Names & Meanings
    • Color Phenomena
    • Color Perception is Individual
    • Color In Fashion
    • Color for your home
    • Color in Space
    • Color Blindness
    • Color Blind Interview
    • Synesthesia
    • Synesthete Deborah Borrowdale-Cox
    • Synesthete Stephen Orr, BH&G Editor
  • Circadian & Light for Health
    • Circadian & THERAPY Topics
    • Circadian Explained
    • Circadian Ganglion Cells
    • Circadian Melatonin
    • Circadian Animals
    • Circadian Research
    • Autism & Lighting for the Spectrum
    • Blue Light Dimming Apps
    • Red Night Lights
    • Vitamin D & Light
    • SAD - Seasonal Affective Disorder
    • Alzheimers and Light Therapy
    • Photosensitivity - Light Sensitive Drugs
    • Red Light Therapy
    • Sleep & Lighting
    • Dreams and Second Sleep
    • NASA - Lighting in Space & Undersea
    • Jet Lag
    • Sunglasses
    • Chakras
    • Crystals, Minerals, & Gemstones
  • Lighting Design
    • LIGHTing Design Topics
    • UV Germicidal Disinfection Light
    • LED Lighting Facts Card
    • CRI - Color Rendering Index
    • LED TM-30
    • LED Kelvin Color
    • LED LPW
    • LED Flicker
    • LED Glare
    • OLED - Organic LED
    • Human Centric Lighting
    • Lighting with Daylighting
    • Lighting for Healthy Buildings & Zero Net Energy
    • Lighting for Healthcare
    • Lighting for Horticulture
    • Lighting for Hospitality & LED Retrofits
    • Lighting for Museums
    • Lighting for Seniors & Low Vision
    • Lighting Design Tips & Codes
    • Parking Lot Lighting
    • Solar Lighting for Humanity & World Health
  • Dark Sky Topics
    • Dark Sky & Light Pollution
    • Dark Sky - Ecology of Night Lighting
    • Dark Sky - Turtle Safe Lighting
    • Landscape Lighting
    • LED Street Lighting Retrofit in Davis
    • Dark Sky Ordinances
    • Dark Sky & Astronomy
    • Dark Sky Reserves
  • Lighting Research & Books
    • Lighting Research
    • Lighting Publications
    • Lighting Education
  • ABOUT ChromaTherapyLight
    • About Topics
    • About Trish
    • Contact & Disclaimer
    • Social Media
    • Newsletter
    • Guidelines for Guest Writers
    • Site Map
  • Davis Insectary Garden
  • Santa Barbara Mesa Insectary Garden