Sleep Timing Disorders and LIGHT

Obeying the Laws of Photobiology

by Madelyn Griffith-Haynie, CTP, CMC, ACT, MCC, SCAC
Part II of a three-part article in the Sleep Series
Click HERE for Part I

Diagram illustrating the influence of dark-light rhythms on circadian rhythms and related physiology and behavior. (Photo credit: Wikipedia)

The influence of dark-light rhythms on circadian cycles, and related physiology and behavior. (Photo credit: Wikipedia)

Keep in mind:

Time cues are what keep our body clocks aligned with the rest of our 24 hour world.

In order for our sleep-wake timing to cooperate with our planet’s day/night cycle, our biological clock seems to need regular environmental time cues — like sunrise, sunset, and/or a stable sleep-wake routine.

The successful shifting of “native” circadian rhythms to those that coordinate with earth’s 24 hour day is calledentrainment.”

Although light is not the only factor acting on our circadian rhythms, many researchers consider it to be the strongest cue for entrainment. Its entrainment effectiveness, however, can be altered by a number of other factors.

  • Regular exercise, for example, when coupled with appropriately timed light exposure, results in a slightly stronger entrainment response.
  • Certain music and supplemental Melatonin (taken at the right time) have also demonstrated a positive effect on entrainment.
  • Stress, on the other hand, weakens the entrainment effect, as do some medications, nicotine, alcohol (or sudden withdrawal from either)

In the rest of this article, we’ll focus primarily on the mechanisms of light entrainment.

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Cooperating with photobiology

SocietyPhotoBiologyPhotobiology — what is it again?

According to Wikipedia,

Photobiology is the scientific study of the interactions of light (technically, non-ionizing radiation) and living organisms.

The field includes the study of [a number of areas, including] visual processing, circadian rhythms . . . and ultraviolet radiation effects.

LIGHT Sleepers

Let’s begin with the first (and part of the second) of the Five Basic Laws of Photobiology I mentioned at the end of Part I:

1. Visible-spectrum light regulates

The therapeutic effects of light depends upon the wavelength transmitted to the brain through the eye’s retina — visible light is the primary regulator of the human circadian response.

2. Only light that is absorbed will have an effect

Otherwise, it can’t be registered — and it matters what kind of light is absorbed when.

What Chronobiologists Currently Believe

Research has strongly indicated that exposure to LIGHT influences human gene expression, hormone secretion, body temperature, heart rate and blood pressure  — as well as cognitive alertness, and sleep.

The body’s suppression of the secretion of the hormone Melatonin in the presence of light – which is fairly easy to measure – is considered a marker of circadian sensitivity.

In the October 2009 issue of Trends in Cognitive Neuroscience, Gilles Vandewalle (Center for the Study of Sleep and of Biological Rhythms at the University of Montréal) noted that light exposure also reduces alpha, theta, and low-frequency brain-wave activity — associated with sleepiness.

  • Since that time, non-sleep specialists seem to have accepted the high probability, at least, that appropriately timed light exposure will have positive effects on our physical and emotional health, as well as helping us to stabilize our sleep timing within the light/dark cycle of our planet — so that we can be alert in the daytime and sleepy at night.
  • Those of us who have trouble with appropriately timed alertness and sleep are believed to be experiencing the effects of a dysregulation of our circadian rhythms, also referred to as chronorhythms.

As I said in Part I of this article, one of the most important reasons for regulating our sleep schedule is to stabilize the quality of light to which we are exposed.

In order for work-arounds (and treatment protocols) for circadian/chronorhythm dysfunctions to be successful, we ALL need to understand and cooperate with what are sometimes referred to as the basic laws of photobiology.

• Visible-spectrum light regulates

Creative Commons: Wikipedia

©Creative Commons: Wikipedia

Light from the visible spectrum seems to be the primary regulator of the human circadian response.

In a human being, the therapeutic effects of visible light (on the day/night cycle, or upon any given organ) depends upon the light wavelength.

Most visible light reaches the human brain through the photoreceptors in the eye’s retina (the thin yellow band leading from in front of the lens, behind the cornea, to the optic nerve in the drawing)

The retina is a light-sensitive layer of tissue lining the eye’s inner surface, connected directly to the rest of the brain through the optic nerve.

The retina and optic nerve are actually brain tissue, part of our central nervous system (CNS) — with several layers of neurons interconnected by synapses.[1][2]

Light Sensitive Neurons

We call neurons that are directly sensitive to light “photoreceptor cells.” Researchers may still discover new categories of bodily processes that are sensitive to a greater range of light (processed by some mechanism yet unknown), but science is currently focused on exploring the effects of the visible light spectrum captured by photoreceptors.

Light below a certain wavelength – 295 nm – is cut off by the cornea, the transparent front part of the eye that covers the iris, pupil, and anterior chamber. [nm=nanometer – one billionth of a meter].

That means that the shortest wavelengths of solar radiation (and the most energetic — all UV-C and some UV-B) are filtered out before they reach the lens.

Since only visible light reaches the retina, the majority of the current scientific thinking is that only visible light is able to affect how the brain registers and interprets light cues.

(Keep in mind that there are scientists exploring light receptors in the skin, with both positive and negative effects on human health, but that arena will not be the focus of this article.)

Visible light “communicates” with the body through two primary pathways, one that governs visual perception and response, and the other that governs “neuro-behavioral” responses, along with hormonal and circadian functions (most sensitive to stimulation from light in the blue spectrum).

How’s Your Secret Decoder Ring?

vintageCrackerJack-226x300For those of us who are not visually blind, the first place things can go “wrong” with our ability to sleep easily and effectively, is some kind of “glitch” in the connections made via the optic nerve that determine how the brain interprets the information it receives.

In other words, some signals from the eye are not getting to the brain intact or timed correctly, possibly due to one or more hypersensitive photoreceptors, visual pathways, or other brain systems that react inappropriately to one or more wavelengths of light.

According to the Wikipedia article on scotopic sensitivity: “A growing number of researchers are taking an interest in the view that inappropriate biochemical processing has the potential to cause physiological and/or visual perceptual problems.”

While the bulk of this research so far has been how the brain interprets light cues visually, as you learn more about how LIGHT affects entrainment, it will be impossible to ignore the possibility that some of us might react atypically to light (and by extension, melatonin) because, in effect, our “Secret Decoder Ring” is off kilter.

Light Response Changes Over Time

For various reasons, response to the effects of the spectrum and intensity of light through-out the human life-cycle demonstrates along a continuum of effect determined by age [Bachem, 1956; Roberts, 2001].

The lens of a baby transmits a small window of the shorter UV-B radiation to the retina, while the elderly lens filters out much of the short visible spectrum blue light wavelength. [Barker et al., 2001] 

LightBrainThat strongly indicates that Baby Boomers and the elderly can be expected to respond differently to light than infants, children, teens, or younger adults.  [Van Someren, 2000b; Yeager et al., 2009; Riemersma-van der Lek et al., 2008; Quinn et al., 1999]

Which means that, no matter what your age, and even if you have been successfully regulating your sleep cycle with light-therapy, to maintain its effectiveness, you can expect to have to tweak it through the years.

• Only light that is absorbed will have an effect

Otherwise, it can’t be registered and interpreted by the brain — and it matters what kind of light is absorbed when.

To have an effect on entrainment, it seems that a specific wavelength of light must be absorbed by a cellular element called a chromophore, which absorbs different wavelengths of light in different parts of the body.

Our eyes, for example, have long been known to have two different areas that absorb chromophores.

  • The light that controls day vision, primarily, is absorbed by the chromophores in the cones (blue, green or red opsins)
  • The light that controls night vision, primarily, is absorbed by the chromophore in the rods (rhodopsin).

Rods and cones determine visual perception and responses — what we are able to see — and are referred to as visual photoreceptors. They communicate with the brain and body through the primary optic tract.

Something NEW Under the Sun

The eye’s anatomy had been well researched for more than a century before the connection between LIGHT and sleep timing was taken seriously by most scientists

despite the fact that a paper had been published in the December 1958 Biological Bulletin by J. Woodland Hastings and Beatrice M. Sweeney —

demonstrating the power of different wavelengths of light to shift circadian rhythm in a certain light sensitive marine animal – with blue spectrum light having the most powerful entrainment effect.

At that time it was widely believed that the biology of human beings was insensitive to the effects of light, so few scientists took much note of it.

Right up until the last decade of the 20th century, most of the science field believed that social factors determined when people went to bed, and thus, fell asleep.

Other than disorders with a visible physical component – such as obstructive sleep apnea – individuals with chronorhythm dysregulations were dismissed as if some flavor of “poor sleep hygiene” underscored all troubles behind the various reportings of “insomnias” of one type or another.

Except among a small community of scientists who were studying sleep architecture, sleep timing, and chronobiology, there was precious little understanding of — or curiosity about — what went wrong when patients weren’t able to adapt their sleep/wake patterns to the rest of the human race — even though a growing number of shift-workers were reporting exactly that.

In the August 8, 1986 issue of the Journal Science, an up and coming sleep researcher, Charles A. Czeisler, PhD, MD (now quite well known as a leading light in sleep research) published a paper of a study that demonstrated that exposure to carefully timed bright light over several days could reset the human circadian rhythm with amazingly precise timing.

But, given what they knew at the time,
science still didn’t understand the mechanism of action. 

AND THAT is where we’ll pick up the trail in the final post of this 3-part article, as we continue to explore Five Laws of Photobiology Affecting Entrainment —  COME BACK for some interesting info about the third of your life that affects how well you function for the rest of it (not to mention, the overall state of your health!)

Articles to come will explain more about sleep timing basics, and will continue to review the basics of sleep and sleep stages, which will underscore the importance of allowing yourself enough time to cycle through them all (and explain WHY some days are harder to manage than others). So stay tuned.

**Primary source for the Laws of Photobiology:
Circadian Rhythm and Human Health,
a paper by Joan E. Roberts, Fordham University. Department of Natural Sciences

Other References for the Sleep Series:

Rhythms of Life, Russell G. Foster and Leon Krietzman
The Promise of Sleep, William C. Dement and Christopher Vaughan
Evaluation and Management of Sleep Disorders, third edition, Martin Reite, John Ruddy, and Kim Nagel

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About Madelyn Griffith-Haynie, MCC, SCAC
Award-winning ADD Coach Training Field founder; ADD Coaching field co-founder; [life] Coaching pioneer -- Neurodiversity Advocate, Coach, Mentor & Poster Girl -- Multi-Certified -- 25 years working with EFD [Executive Functioning disorders] and struggles in hundreds of people from all walks of life. I developed and delivered the world's first ADD-specific coach training curriculum: multi-year, brain-based, and ICF Certification tracked. In addition to my expertise in ADD/EF Systems Development Coaching, I am known for training and mentoring globally well-informed ADD Coach LEADERS with the vision to innovate, many of the most visible, knowledgeable and successful ADD Coaches in the field today (several of whom now deliver highly visible ADD coach trainings themselves). For almost a decade, I personally sponsored and facilitated seven monthly, virtual and global, no-charge support and information groups The ADD Hours™ - including The ADD Expert Speakers Series, hosting well-known ADD Professionals who were generous with their information and expertise, joining me in my belief that "It takes a village to educate a world." I am committed to being a thorn in the side of ADD-ignorance in service of changing the way neurodiversity is thought about and treated - seeing "a world that works for everyone" in my lifetime. Get in touch when you're ready to have a life that works BECAUSE of who you are, building on strengths to step off that frustrating treadmill "when 'wanting to' just doesn't get it DONE!"

10 Responses to Sleep Timing Disorders and LIGHT

  1. Pingback: Sleep Timing and Time Tangles | ADD . . . and-so-much-more

  2. Just booked mark a few of your blogs about sleep! Looking forward to going through them all one night when the dawn creeps through my window. Thank you for directing me to them,


    • You are MOST welcome. I hope you find them interesting (and at least SOME of the helpful).

      Its a lot of neuroscience, but I have found that truly understanding what’s going on in the brain “de-personalizes” some of our experiences, helping to distance ourselves enough to put some new strategies in place as a result of the overlap of what you learned and what you personally experience.

      It’s planned to be an ongoing series — HUGE topic!

      Thanks for taking the time to check them out – and comment! (thanks, too, for all your “likes”)


  3. Pingback: The Trials and Tribulations of Engaging Learning In An Owl With PDA | Pathological Demand Avoidance Syndrome an autistic spectrum disorder

  4. Dr. Rex says:

    Reblogged this on It Is What It Is and commented:
    Additional information about the need to have adequate sleeping hygiene in our lives!!! Great reporting job!!!


    • WOW – you really DO appreciate the importance of sleep! Thank you for helping me get the word out by reblogging.

      click over to see what Dr. Rex has to say about sleep (search for it to get a blogroll of her articles). Similar to the variety of topics here on ADDandSoMuchMore, she blogs about a variety of topics on It is What it Is. If you like what I do, you’ll like what she does. Check out her bio on the ABOUT page. She’s a world-changer.


  5. “Other than disorders with a visible physical component – such as obstructive sleep apnea – individuals with chronorhythm dysregulations were dismissed as if some flavor of “poor sleep hygiene” underscored all troubles behind the various reportings of “insomnias” of one type or another.”

    You’ve written this in the past tense: “were dismissed”. Unfortunately, the vast majority of doctors, including most “sleep doctors”, still have absolutely no understanding of circadian rhythm disorders (or, as you call them, chronorhythm dysregulations).

    Those of us with circadian rhythm disorders (CRDs) are sooo tired of hearing about (being accused of) insomnias and bad sleep hygiene! After years and decades of suffering from these disorders, people are now discovering that they are not alone; it is a life-changing revelation. Wikipedia and the rest of the internet, yourself included, are to be thanked for this.


    • @ Delayed2Sleep

      RE: “those of us with CRDs etc.” YOU SAID IT! I, too, am OVER it (and I am a charter member of the club, btw)

      To”day,” for example, I did not awaken until 11pm E. I am off-phase again, even for *my* DSPS N-24 (4am sleep – 12 noon wake-up is what I try my darndest to maintain) — which means, even though I was unable to sleep “yesterday” until after 11am the following day, almost 14 hours unconscious! (for part of MY story, see JetLagged for Life [<==link])

      My use of “chronorhythm dysregulations” is intentional – I don’t want to encourage doctors to look up “Disorders” in the DSM-V (don’t get me started on that!) and dismissing everyone who doesn’t fit neatly into one of the labels.

      If our sleep timing is dysregulated in any fashion, that needs attention, IMHO, even if we turn out to be unique in our presentation.

      I’m glad you caught the past tense. You are absolutely correct that “the vast majority of doctors, including most “’sleep doctors’” still have absolutely no understanding of circadian rhythm disorders.” In this case I was referring to the scientific community — i.e., those who were doing *research.* Until the researchers got a clue, there was no way the sleep doctors were likely to look beyond “sleep hygiene.”

      Thanks so much for all YOU do to get the word out, and for ringing in here.
      “It takes a village to educate a world”

      If you are struggling with Delayed Sleep Phase Syndrome (or “disorder” – DSPS or DSPD) or Non-24 sleep/wake (N-24), click delayed2sleep’s name above the comment and go read about yourself — GREAT site!

      Link also ALWAYS available from my Sleep Links post [<==link] — scroll DOWN to "Circadian Rhythms (etc) and click on [linked here too ==>]"Owls of the World, Unite!" to jump to the site. Browse their GREAT content from there.


  6. Reblogged this on Broken Brain – Brilliant Mind and commented:
    Very true. Light seems to be designed to wake us up and get us moving. I have light-blocking curtains in my bedroom, which has done wonders for my sleeping patterns.

    Now, if can can figure out a way to get to bed at a decent hour, instead of whiling away the hours watching mindless television…


    • Thanks for the reblog, BB.

      RE: TV at night – try NOT watching – meaning, just listen as you attempt to drowse – throw a cover over the screen to block the light (blue spectrum, remember). It’s worth a shot.

      Best, btw, is to cut an old blanket to slightly larger than screen size, and rubber-band each of the corners to make it “grab” – that way most of the light is blocked, but the electronics can still “breathe.”

      Thanks always for your support.

      TBI readers (including PTSD, btw) – click his link and check out his site – GREAT info from the trenches. BTW – you can always find a link to his site from the right column – scroll DOWN and click on “Broken Brain- Brilliant Mind”


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