Your circadian rhythm
determines the quality of your sleep.
Q: What is the “circadian rhythm?”
Answer: Your body keeping its own time, using its own clock.
Your body’s internal clock system synchronizes itself to the world via several environmental signals.
determine the quality of your circadian rhythm.
With few exceptions, all life developed “under bright days and dark nights” (source).
Melatonin is not unique to humans. It’s not unique to mammals. It’s in amphibians, birds, reptiles, cockroaches, insects, spiders, unicellular organisms, bacteria, plants – every plant that has been studied contains melatonin. Every organism contains melatoninRussel Reiter, PhD
These environmental signals (brightness & darkness) synchronize your body’s circadian clock.
More than any other variable, light drives your body clock.
— Much more than exercise, much more than the diet.
While your skin does have photoreceptors that sense environmental light — the eyes have 100x more photoreceptors than skin.
The eyes are the windows to the circadian soul.
The light in your environment — along with only a few other factors — holds the keys to mastery of your circadian rhythm.
Those other variables include:
- clean air & healthy buildings
- a calm mind
- meal timing
- gut health
— but light is circadian royalty. Nothing else, by itself, comes close.
Light, the Most Important
Environmental stimuli signaling the progression of time are known as zeitgeber, a German word meaning “time giver,” and include light as the most prominent signal, as well as others, such as patterns of exercise, food consumption, social activity, and more.https://journals.lww.com/cmj/Fulltext/2021/03200/Light_therapy__a_new_option_for_neurodegenerative.2.aspx
The most important zeitgeber (from German, something that “gives time”) reaching the SCN is ambient light in the environment.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6751071/
Light during the day and darkness at night are crucial factors for proper entrainment of the human circadian system to the solar 24-h day.https://pubmed.ncbi.nlm.nih.gov/28637029/
Melatonin is the hormone of sleep. It rises, you sleep. It falls, you are alert.
- Melatonin has all sorts of benefits: it’s anti-cancer, it promotes immunity, it’s anti-inflammatory, and protects the gut microbiome from pathogens.
In the modern world, melatonin cycles tend to be weak — and failing.
To promote sleep — and promote other benefits — melatonin must rise high in the evening and stay high all night.
But it’s not as simple as taking melatonin supplements.
No, in order to rise high at night, melatonin must be low all day.
It’s a cycle — without one, you can’t have the other.
Drops in the Morning
Low all day
Melatonin crashes in the morning — allowing you to wake up — releasing you from the powerful grip of drowsiness.
If melatonin stays high, you’ll keep sleeping, feel sluggish & groggy, and have trouble getting going.
Melatonin — Rises after Dark
High all night
Melatonin rises at nighttime, just before bed — forcing your body into both 1) wanting sleep, and 2) easily falling asleep.
Chronic disruptions of circadian rhythm may have the potential to seriously affect human health.
For instance, decrease of melatonin levels plays an important role in development of chronic diseases and conditions such as cancer 61, 80, 81, 82, 83, cardiovascular diseases 83, reproduction 84, endometriosis 84, gastrointestinal and digestive problems 85, diabetes 86, 87, obesity 88, depression 89, sleep deprivation 90, bipolar spectrum disorders 91, and cognitive impairment 92.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
How We Tell Solar Time
The body’s clock keeps time on its own, but it’s always receiving clues — from the environment — about the time of day.
There is a time, each day, called “solar noon.” This is when the sun is the highest in the sky, where you are.
- Sunrise is when “daytime” begins
- Sunset is when “nighttime” begins
Research has confirmed — again and again — that a healthy circadian rhythm is one that aligns closely to natural sunlight cycles.
When the sun is up, it’s important that your eyes (and skin) see bright light.
And when the sun is down, it’s important that your eyes (and skin) see darkness.
A healthy melatonin cycle should align perfectly with natural sunlight cycles: when the sun is up –> melatonin is down.
The further our body’s cycle gets away from “solar time,” the worse the outcomes for our health.
How do we become out of sync with solar time?
- Sleeping in: Missing critical hours of sunlight each morning
- Bright light at night
- Staying indoors all day
- Staying up light
Staying in sync with solar time is an important foundation of longevity — it’s a methodology that is essential to maintaining proper melatonin levels: low in daytime, high at night.
Three types of light keep melatonin levels optimally healthy.
Let’s dive into the mystery and magic of light. Learn to master this most important circadian muse.
Enjoy the direct benefits of morning light.
- Do you want astronomical levels of healing for your circadian rhythm — and, therefore — entire body?
Bright morning light starts each day perfectly — no matter what happened yesterday.
There are three major reasons we need morning sunlight:
- Morning light suppresses morning melatonin — allowing you to wake up and start your day
- Morning light starts your circadian rhythm
- Morning light raises serotonin — which will be converted to melatonin at night
Without serotonin, melatonin cannot be produced at night — meaning your sleep will suffer.
Serotonin is an incredibly important hormone during the day, too — don’t be fooled by internet experts.
Without a habit of receiving your bright morning light, your other attempts to be healthy, lose weight, feel better — or sleep better — will only be playing catch up.
As we’ll prove, the sheer power of bright morning light — for your brain chemistry, hormones, metabolism, and future circadian rhythm — are nothing short of astounding.
You’ll notice, too, when you try this for yourself: The benefits of morning light are so great that nothing can replace it. No other hack can do what it does, and once you’ve missed morning light, it’s gone for today.
But you don’t have to miss it! Start receiving morning light — first thing tomorrow morning — and make it a life-long habit that never once regret.
Why should you decide to get morning light each day?
Let’s explore the science…
Natural light exposure — beginning with morning light — “rapidly” resets the circadian rhythm.
Further, we demonstrate that earlier circadian timing can be rapidly achieved through natural light exposure during a weekend spent camping.https://pubmed.ncbi.nlm.nih.gov/28162893/
Camping — which is spending 24 hours outdoors — shifts the circadian rhythm forward, aligning the modern body with solar time.
We also show that circadian and sleep timing occur earlier after spending a weekend camping in a summer natural light-dark cycle…
…compared to a typical weekend in the modern environment.https://pubmed.ncbi.nlm.nih.gov/28162893/
Morning light, by itself, directly stabilizes the circadian rhythm.
Our results indicate that bright blue-enriched morning light stabilizes circadian phase, and it could be an effective counterstrategy for poor lighting during the day and also light exposure at the wrong time, such as in the late evening.https://pubmed.ncbi.nlm.nih.gov/28637029/
Bright morning light lowers melatonin. Melatonin should be low in the morning.
The [morning] decline of melatonin levels was significantly greater after the exposure to [morning] blue-enriched white light.
Exposure to [morning] blue-enriched white light significantly improved subjective perception of alertness, mood, and visual comfort.https://pubmed.ncbi.nlm.nih.gov/30674951/
Bright morning light causes melatonin to rise earlier this evening — and facilitates an earlier wake up tomorrow morning.
The bright light treatment advanced the evening rise in plasma melatonin and the time of sleep termination.https://pubmed.ncbi.nlm.nih.gov/2912203/
A natural summer light cycle — with bright, early mornings — “entrains” your body’s circadian clock to solar time.
Exposure to a natural summer (14.5 hours of daylight, 9.5 hours of darkness) light-dark cycle entrains the human circadian clock to solar time, such that the internal biological night begins near sunset and ends near sunrise https://pubmed.ncbi.nlm.nih.gov/28162893/
Bright morning light decreases cortisol — a hormone of stress, weight gain, and insomnia.
Interestingly, the morning bright light exposure… decreased plasma cortisol.
During the bright light session, subjective sleepiness decreased irrespective of the room temperature.
Melatonin and cortisol are “classical markers of the circadian rhythm.” Why? Because melatonin makes you sleep, and cortisol wakes you up.
Bright morning light directly raises melatonin in the morning, and then calms the naturally high cortisol that wakes us up in the morning.
The classical markers of the circadian system (melatonin and cortisol)https://pubmed.ncbi.nlm.nih.gov/30674951/
Bright morning light is essential for daytime alertness.
Blue-enriched LED light seems to be a simple yet effective potential countermeasure for morning drowsiness and dozing off in class, particularly in schools with insufficient daylight.https://pubmed.ncbi.nlm.nih.gov/30674951/
Bright morning light restored circadian & body temperature cycles in patients with chronically delayed sleep rhythms.
Bright light has recently been shown to have phase-shifting effects on human circadian rhythms. In this study we applied this effect to 20 patients with delayed sleep phase syndrome (DSPS) who were unable to fall asleep at conventional clock times and had a problem staying alert in the morning. In a controlled treatment study, we found that 2 h of bright light exposure in the morning together with light restriction in the evening successfully phase advanced circadian rhythms of core body temperature and multiple sleep latencies in these patients. This finding corroborates the importance of light for entraining human circadian rhythms.https://pubmed.ncbi.nlm.nih.gov/2267478/
Winter depression can be treated effectively with bright morning light.
Bright light exposure has been found to alleviate the symptoms of recurrent winter depression in many patients.
Morning light was found to be significantly better than evening light in reducing depressive symptoms.https://pubmed.ncbi.nlm.nih.gov/2322085/
Seasonal affective disorder (SAD) patients often have delayed circadian rhythms — and morning bright light therapy helps.
Our findings suggest that patients with winter depression have circadian rhythms that are abnormally delayed and that bright light therapy benefits winter depression by providing a corrective advance.https://pubmed.ncbi.nlm.nih.gov/2322085/
Bright light at night helps winter depression, but morning light is much better.
According to the phase-shift hypothesis for winter depression, morning light (which causes a circadian phase advance) should be more antidepressant than evening light (which causes a delay).
These results should help establish the importance of circadian (morning or evening) time of light exposure in the treatment of winter depression. We recommend that bright-light exposure be scheduled immediately on awakening in the treatment of most patients with seasonal affective disorder.https://pubmed.ncbi.nlm.nih.gov/9783559/
Bright morning light is most effective when it mimics natural sunlight. Morning sunlight is magical for promoting health.
Light exposure elicits numerous effects on human physiology and behavior, such as better cognitive performance and mood.
However, after both SR [sleep restricted] nights, mood and well-being were significantly enhanced after exposure to morning DsL compared with DL [dim light] and [bright light].
Our data indicate that exposure to an artificial morning dawn simulation light improves subjective well-being, mood, and cognitive performance,
Thus, DsL [dawn-simulating light] may provide an effective strategy for enhancing cognitive performance, well-being, and mood under mild sleep restriction.
(light was: starting 30 min before and ending 20 min after scheduled wake-up time )https://pubmed.ncbi.nlm.nih.gov/23841684/
Bright morning light treats insomnia, premenstrual syndrom, and seasonal affective disorder.
The melatonin rhythm phase advancement caused by exposure to bright morning light has been effective against insomnia, premenstrual syndrome, and seasonal affective disorder (SAD).https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2290997/
Healthy light improves the gut microbiome. Morning light is rich in beneficial red and near-infrared light freqe.
Results: Recent work by our research group has demonstrated that PBM (red and NIR light) delivered to the abdomen in mice, can alter the gut microbiome in a potentially beneficial way. This has also now been demonstrated in human subjects.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6859693/
Morning light is the safest and most beneficial source of natural light.
Controlled exposure to either daylight or a comparable source of artificial light, and has been reported to be an economic, convenient, safe, and effective way to ease symptoms of sleep disorders, depression, and cognitive disorders.https://journals.lww.com/cmj/Fulltext/2021/03200/Light_therapy__a_new_option_for_neurodegenerative.2.aspx
Getting morning light is incredibly easy, if you have or allow time for it.
First, on sunny mornings, simply be outside in the sunlight.
Face in the general direction of the sun as it rises — looking safely toward it, but not at the sun.
Throughout the morning, find moments to step outside and do the same — allowing the bright morning light to bathe you: your eyes, and as much skin as you can bare.
Sunlight through windows is a valid option when actually going outside is not realistic due to weather or obligations.
Second, in poor weather, have an indoor option: use artificial light to re-create morning sunlight.
Incandescent bulbs best — and nearly perfectly — re-create morning sunlight. Examples of great incandescent bulbs include:
- 250w heat lamps
- 150w clear incandescents
These bulbs are easily screwed into a typical hardware clamp lamp, and attached onto a book shelf or other furniture.
Weak daylight shifts your circadian rhythm backward.
Do you want:
- healthy (low) melatonin levels all day?
- to feel awake and alert all day?
- higher dopamine levels?
- higher evening melatonin?
- a strong circadian rhythm?
- better digestion?
If you do, there’s no substitute for bright daylight. No other hack can replace — or mimic — what bright daylight does for your body.
Reduced exposure to daytime sunlight and increased exposure to electrical lighting at night leads to late circadian and sleep timing.https://pubmed.ncbi.nlm.nih.gov/28162893/
Your Daytime Melatonin
Historically, humans spent their days and nights outside.
This is no longer true — modern humans spend 93% of their time indoors (source).
As such, we receive bother brighter light and night — and weaker light during the day.
It simply isn’t economically feasible for most buildings to re-create healthy sunlight indoors. (And using modern bulbs, it isn’t possible).
Modern life and work styles have led to much more time spent indoors, often with lower daytime and higher evening/nighttime light intensity from electrical lighting than outdoors.https://pubmed.ncbi.nlm.nih.gov/28637029/
Melatonin in Healthy Sunlight
Healthy light — like sunlight — suppresses melatonin all day.
Melatonin in Unhealthy Light
Indoor lighting doesn’t drive down melatonin like natural light.
The end result? Modern melatonin cycles are weak! We’re sleepy all day, and don’t sleep as deeply at night.
Light cycles have changed dramatically — and so has our sleep, with all of its restorative benefits.
Why should you care about bright daylight, each day?
Force your melatonin to rise higher — step out into the sunlight throughout the day.
Repeated exposures to daytime bright light are effective in controlling the circadian phase and increasing the peak level of nocturnal melatonin risehttps://pubmed.ncbi.nlm.nih.gov/16840653/
Bright daylight — even while napping — protects your nightly melatonin levels.
One late night can disrupt the circadian rhythm. When daytime napping the next day, bright lights can signal ‘daytime’ — even to the sleeping brain.
To enhance melatonin secretion and to maintain their conventional sleep-wake cycle, after night work, shift workers should sleep during the daytime under bright-light conditions rather than dim-light conditions.https://pubmed.ncbi.nlm.nih.gov/29144169/
Daytime blue light exposure has an acute preventive impact on nocturnal light‐induced melatonin suppression.
The preventive effect of blue daytime light has proven more efficient than other wavelength composition of daylight.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Bright daytime light raises melatonin and improves immunity.
Bright light exposure during the daytime enhances the nocturnal melatonin increase and activates the mucosal immune response.https://pubmed.ncbi.nlm.nih.gov/10373104/
Bright daylight improved daytime sleepiness, fatigue, and cognition — when combined with evening melatonin supplements.
The combined bright light and melatonin treatment improved subjective daytime sleepiness, fatigue, and cognitive function in the 3-month study.https://pubmed.ncbi.nlm.nih.gov/24132057/
Bright light helps prevent nearsightedness.
There’s another part of sunlight that could help prevent myopia: exposure to visible bright light. Even on a cloudy day, visible light outdoors is at least 10 times brighter than the light indoors.https://www.sciencedaily.com/releases/2014/11/141120112348.htm
Sunlight drastically reduces the risk of nearsightedness in children.
The “outdoor effect” on nearsightedness, or myopia, is a longstanding observation backed by both scientific and anecdotal evidence.
It’s so compelling that some nations in Asia, which have among the highest myopia rates in the world, have increased the amount of daily outdoor time for children in the hopes of reducing the need for glasses.
“Data suggest that a child who is genetically predisposed to myopia are three times less likely to need glasses if they spend more than 14 hours a week outdoors,” says optometrist Donald Mutti, OD, PhD, of The Ohio State University College of Optometry.https://www.sciencedaily.com/releases/2014/11/141120112348.htm
Bright outdoor light releases dopamine — improving mood, brain function, creativity, and eyesight.
When exposed to outdoor light, specialized cells in the retina help control how big or little the pupil dilates to let more or less light in. The cells connect to others that release dopamine — an important neurotransmitter in the eye and brain.https://www.sciencedaily.com/releases/2014/11/141120112348.htm
Bright day-time light improves dinnertime digestion.
In a previous study we found that daytime exposure to bright as compared to dim light exerted a beneficial effect on the digestion of the evening meal.
[However,] the exposure to dim light in the evening exerts a better effect on carbohydrate digestion in the evening meal than does the exposure to bright light.https://pubmed.ncbi.nlm.nih.gov/14535358/
Three Points: 1) Cloudy days are brighter than indoor lighting. 2) The circadian rhythm is “best cued by natural bright light.” 3) Dim indoor lighting is harmful to health.
Melatonin suppression in humans was observed by applying bright light of 2500 lux, much brighter than indoor lighting, but much less so than a cloudy day. Therefore, it was concluded that the circadian rhythm is best cued by natural bright light and would be insensitive to dim indoor lighting.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Blue light is stronger than green light for “awakening, alert” brain activity.
Experimental subjects had quicker auditory reaction times and fewer lapses of attention under blue light than green light
Blue wavelengths suppressed sleep‐associated delta brainwaves better than green wavelengths and boosted the alpha wavelengths, which are related to alertness
This suggests that short wavelengths, perceived as blue color, might be used to control sleepiness.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Dim (daytime) indoor lighting disrupts your circadian rhythm.
Therefore, inadequate low lighting, especially lacking the blue part of the spectrum, may cause circadian rhythm disruptions.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Exposure to blue light during the day is important to suppress melatonin secretion, the hormone that is produced by the pineal gland and plays crucial role in circadian rhythm entrainment.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
How can you optimize your daytime light?
A few key steps will safeguard your circadian health, each day.
First, maximize daily outside time.
The more, the better! Bright outdoor light will constantly, and perfectly, remind your brain chemistry and hormones where you are in the 24-hour day. The more time you spend outside, the better your sleep will be. Don’t wear sunglasses very often, they block the very brightness and frequencies needed to ‘entrain’ your circadian rhythm.
The outdoors are always a premier option for restoring health. Almost always more healthy than the indoors, being outdoors is a good idea for a plethora of reasons, not just the circadian benefits.
Second, take your breaks outside.
When you reach your (hopefully frequent) break times, step outside. Even a few minutes of bright sunlight send strong signals, entraining your circadian rhythm. Whether at work, or at home — a few minutes outside throughout each day is pure dynamite for your health.
Third, have an indoor-lighting strategy.
Utilize strong, incandescent lights to illuminate spaces indoors where you spend lots of time. This can be immensely valuable, especially, during rainy days and long, dark winters.
Workspaces, the couch — feel free to spend time under bright light each day.
Take action! Work wonders toward your ability to 1) fall asleep, 2) stay asleep, and 3) wake up refreshed.
Use bright light to optimize the immune, metabolic, digestive, cognitive, and longevity benefits of robust circadian rhythm.
~ 3 ~
Protect Yourself After Hours
Kryptonite For Your Sleep
Blue light is high-energy light, and it directly blocks your brain’s melotonin production.
Instead, blue light at night raises cortisol — the hormone of alertness, a hormone of stress.
The effects of late blue light are not short-lived. As we’ll show, blue light before bed will affect your entire night of sleep, continuing up to 24-hours later.
Blue frequencies are very near the spectrum of ultraviolet (UV) light — an extremely short-wave, high-energy radiation.
Red light is lower energy. Blue light is high energy.
Melatonin — rising in darkness — induces sleep,
and facilitates all metabolic, endocrine, and immune nighttime functions.
The light-inhibited production of melatonin conveys the message of darkness to the [brain]clock and induces night-state physiological functions, for example, sleep/wake blood pressure and metabolism.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6057895/
All light suppresses melatonin — including artifical light.
In modern society exposure to artificial lighting is virtually unavoidable.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Do we want low melatonin levels?
Deficiency of nighttime melatonin is linked to major health complicaitons.
Decrease of melatonin levels plays an important role in development of chronic diseases and conditions such as cancer 61, 80, 81, 82, 83, cardiovascular diseases 83, reproduction 84, endometriosis 84, gastrointestinal and digestive problems 85, diabetes 86, 87, obesity 88, depression 89, sleep deprivation 90, bipolar spectrum disorders 91, and cognitive impairment 92.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
The circadian rhythm is essential for life. If it is not preserved, serious diseases might develop. Light and its role in synchronization, but also in disruption of the circadian rhythm is discussed.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Low nighttime melatonin = highest risk
Studies consistently suggest that women with the lowest concentration of the main melatonin metabolite sulfatoxymelatonin, have the highest risk for breast cancer.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Light is bioactive. The most important aspect of blue frequencies is its impact on the circadian rhythm.
Thus, today it is understood that blue light has many physiologic effects but perhaps the most important among them is to entrain the circadian rhythmhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Blue frequencies are the strongest ‘synchronizing agent’ for the circadian rhythm.
Short wavelengths, perceived as blue color, are the strongest synchronizing agent for the circadian system that keeps most biological and psychological rhythms internally synchronized.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Even small amounts of blue light at night 1) disrupt the circadian rhythm 2) with severe health implications.
Exposure to low levels of blue of light as well as bright light during night or before bed time may disrupt the circadian rhythm with severe general health implications. At the same time blue light exposure during daytime is crucial for the vitality of the organisms.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Light’s biological effects aren’t constant. In the evening, less is more.
Chronic light exposure at the wrong time, at night during shift work for example, may contribute to shifts of the circadian clock phase 59, dependent on duration, wavelength, and intensity of lighthttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Blue-rich light suppresses melatonin significantly more than incandescent light.
For low light levels (40 lx), the melatonin suppression is significantly greater 69 after 2 hours of exposure in the evening to blue‐rich (6500 K, CFLs light) than to incandescent light (3000 K).https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Bright nocturnal light has been shown to suppress melatonin secretion.
The human circadian system is sensitive to short wavelength light [blue].https://pubmed.ncbi.nlm.nih.gov/26777427/
Even low levels of normal light in homes can disrupt the circadian rhythm.
A comparison between the effects of living room light (less than 200 lux) and dim light (about 3 lx) before bedtime showed that even low levels of light in house settings may be sufficient for circadian disruptions in humans: Exposure to room light suppressed melatonin levels and shortened the duration of melatonin production in healthy young subjectshttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
The body is more sensitive to blue light at night than in the morning.
the alerting effect of light sources with a prominent blue peak appeared to be stronger in the evening and night, compared to morning hours.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
E-books that emit light suppress melatonin, and delay the circadian rhythm.
Reading a light emitting e‐book before sleep, as compared with printed book, increased the time to fall asleep 73 in young adults (25 ± 3 years old).
In individuals reading e‐books before bed‐time, their circadian clock was delayed, assessed by delayed and reduced phase of rapid eye movement sleep.
Melatonin blood concentration levels were suppressed and alertness on the next morning was reduced.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
The circadian rhythm affects metabolism (body temperature), sleep, cognition, and “countless other physiological variables [that] exhibit daily oscillations.”
Body temperature, hormonal levels, sleep duration and quality, cognitive performance and countless other physiological variables exhibit such daily oscillations.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Blue light was unknown as a circadian signaller until 1998.
It was not until 1998, when a new type of photoreceptor in the human eye was discovered 2 and later identified to be especially sensitive to blue light. Importantly, these new photoreceptors are retinal ganglion cells (RGCs) and communicate directly with the brain.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Strong, daytime blue light is good. All evening blue light is bad — though more is worse.
The beneficial effect on circadian synchronization, sleep quality, mood, and cognitive performance depends not only on the light spectral composition but also on the timing of exposure and its intensity.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
While the exposure to blue is important for keeping organism’s wellbeing, alertness, and cognitive performance during the day, chronic exposure to low‐intensity blue light directly before bedtime, may have serious implications on sleep quality, circadian phase and cycle durations.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Blue light before bed severely affects children.
In children, bright light before bedtime has a robust melatonin suppressing effect… We further found that melatonin levels remained below 50% baseline for at least 50 min after the end of light exposure for the majority.https://pubmed.ncbi.nlm.nih.gov/34997782/
Orange light before bed is less harmful than blue light.
During the night, participants had longer total sleep times after orange light exposure than after blue light exposure in the evening.https://pubmed.ncbi.nlm.nih.gov/28637029/
Un-natural light cycles are profoundly linked to obesity and metabolic syndrome.
In recent years, humans have shifted away from the naturally occurring solar light cycle in favor of artificial and sometimes irregular light schedules produced by electric lighting. Exposure to unnatural light cycles is increasingly associated with obesity and metabolic syndrome;https://pubmed.ncbi.nlm.nih.gov/23929553/
Findings from a number of studies suggest that mistimed light exposure disrupts the circadian rhythm in humans, potentially causing further health impacts.https://pubmed.ncbi.nlm.nih.gov/23929553/
Even dim light at night harms the liver.
Exposure to dimly illuminated, as compared to dark, nights decreased the rhythmic expression in all but one of the core circadian clock genes assessed in the liver.https://pubmed.ncbi.nlm.nih.gov/23929553/
Additionally, mice exposed to dim light at night attenuated Rev-Erb expression in the liver and adipose tissue.https://pubmed.ncbi.nlm.nih.gov/23929553/
Even dim light at night alters eating habits and leads to weight gain.
[Dim light at night-induced] Changes in the circadian clock were associated with temporal alterations in feeding behavior and increased weight gain.https://pubmed.ncbi.nlm.nih.gov/23929553/
Even mild changes in environmental lighting can alter circadian and metabolic function.
These results are significant because they provide evidence that mild changes in environmental lighting can alter circadian and metabolic function.https://pubmed.ncbi.nlm.nih.gov/23929553/
Red light barely affects melatonin at all — yet blue light crushes melatonin levels.
How can you optimize your evening light?
First, understand what optimal looks like.
Optimal is almost certainly this: complete darkness after sundown, with the exception of light from fire.
This isn’t naturalistic idealism: Fire produces almost entirely red/orange light — which has only minimal effect on the circadian rhythm.
It’s plain to see that prior to electricity, the only terrestrial evening light humans had access to was that: fire!
First, see what’s optimal — to allow melatonin to rise unimpeded — and then, let’s work back from there.
Second, take stock of your current evening light exposure.
At home, at work, at late-night events — how is the lighting?
Many homes and offices have harsh LED and fluorescent bulbs, which get used at night.
If you’re exposed to bright lighting at night, you have two options:
- Change your environmental lighting — use lamps with dimmer, warmer bulbs
- Wear eye protection that filters blue light
Third, improve your environmental light.
Most modern environments have unhealthy light at night — which means we all have room to improve!
Changing your environmental lighting means, first, turning off the harsh daytime lighting at night. Use bright light at night only when absolutely necessary — to protect your melatonin levels and sleep quality.
Our devices are unfortunately rich in blue light. Reducing the brightness and harshness on TVs, computers, and smart phones is an important step toward healthy environmental light.
Fourth, consider wearing some eye protection.
Wearing eye protection involves wearing glasses that reduce blue light to the eyes.
If lenses are to successfully filter out much blue light, they must be tinted themselves — either yellow, orange, or red. The deeper and warmer the tint, the more blue they’ll filter out.
If “blue filtering” lenses are essentially clear, they’re only reducing a small portion of blue light, and not enough to protect your melatonin levels at night.
In my experience, there’s no need to become a blue light-obsessed maniac. It isn’t critical to find wrap-around glasses to block all peripheral light (unless spending extended time in harshly-lit big stores at night).
While blocking more blue light will almost certainly improve nightly melatonin levels, stressing about blue light will harm you more than the blue light itself.
A Word About Stress Hormones
Whatever steps you take to reduce blue light — whether with new light bulbs or protective eyewear — take it all in stride.
Every little change you make helps, so there’s no need to feel stress and, in fact, any stress you feel over this is worse than the presence of blue light.
How do we know this? Cortisol is a hormone of wakefulness, a primary signaller of the circadian rhythm. Elevating your stress hormones (like cortisol) at night directly lowers melatonin.
You may need — and immensely benefit from — higher evening melatonin. But worrying and stressing about imperfection will only take you further from that.
So do what you can to improve your health, but don’t stress about it.
By now, you should understand how important each of these three concepts are.
- Morning light starts the circadian rhythm
- Daylight keeps melatonin low
- Proper evening light forces melatonin to rise
…and all of these work together to balance hormones, nourish brain chemistry, support the metabolism, and control weight.
We’ve also seen just how optimal nature’s light cycle is, from sun up, to sundown, and all evening.
So what, then, can healthy light cycles do for you?
- What can early sunrises do for you?
- What can darker evenings do for you?
- What can daily sunlight do for you?
Let me share my story.
Understanding and mastering my light environment has provided exponential increase to my health.
Deeper sleep each night has allowed me to wake up more refreshed, more energized, and earlier every day!
My brain function is sharper and quicker. My creativity is higher.
As a musician, I noticed I was able to retain ideas quicker, and for a longer time. Gigs became less stressful, and more fun.
Good sleep — directly as a result of minding my light environment — improved my digestion, metabolism, & inflammation, and helped me feel more interested in socializing as an ambivert.
Things just got easier.
Remember, there are no silver bullets with health. They virtually never exist — and your light environment is far from the only variable that matters.
And I tested each variable independently, to see how much each affected me.
And of course the opposite is true: Any time I’ve gotten off track with my light cycles and sleep, I’m reminded of their importance by feeling worse.
Everything — no matter your goal — is harder when sleep is suffering.
And your light cycles directly impact your sleep. Whatever you do, healthy light cycles will improve it, strengthen it, and nourish it.
At the end of our life, there are some things we’ll never regret doing — being kind to our loved ones, speaking words of life into our friends, and forgiving mistakes all come to mind.
Some other things we likely won’t regret — but instead will serve us and our loved ones immensely: waking up early and taking in the sunrise, stepping out into the light throughout the day, and turning the lights down a bit at night.
To continue in SLEEP, select Meal Timing:
More interesting quotes:
A simple solution that may effectively block and reduce the blue portion of the light spectrum before bedtime are blue light blocking glasses and lenses 116, 117. Wearing blue light blocking eyewear before 118, 119 and during 120 bed time may effectively attenuate LED induced melatonin suppression 121, 122 and thus can potentially facilitate the adaption to new social schedules 123 and reduce sleep disturbances and their consequences among the general population.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
We demonstrate that earlier circadian timing can be rapidly achieved through natural light exposure during a weekend spent camping.https://pubmed.ncbi.nlm.nih.gov/28162893/
Rather recently, the availability of artificial light has substantially changed the light environment, especially during evening and night hours. This may increase the risk of developing circadian rhythm sleep–wake disorders (CRSWD), which are often caused by a misalignment of endogenous circadian rhythms and external light–dark cycles. While the exact relationship between the availability of artificial light and CRSWD remains to be established, nocturnal light has been shown to alter circadian rhythms and sleep in humans.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6751071/
It is apparent that there are two key components to keep a healthy circadian system: An increase in the blue portion of the artificial light during daytime should be accompanied with a reduction of the same blue portion of artificial light during the night and evening hours.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
Note: I like the above quote because it demonstrates how easy it is to understand healthy lighting: brighter in the daytime and darker (less blue) at night!
But it also is a dramatic oversimplification that, by itself, ignores the big picture: harsh, blue-rich LEDs are shown to have numerous, and significant problems: for the eyes, for the skin, for brain chemistry, hormones, and more.
The problem with blue-rich modern bulbs isn’t so much the intense blue light present, but instead, what’s missing.
Sunlight is blue-rich, but is perfectly balanced by an equal amount of nourishing red light — and roughly 5X the infrared of blue. These wavelengths appear to dramatically protect the body (skin/eyes/brain) from the harshness of rich blue light.
Further, for several hours out of the day — morning and evening — blue light is dramatically filtered out of sunlight, leaving behind healthy reds and oranges, along with restorative infrared light.
With this in mind, the above quote is modified by this very wise statement from the same researchers:
Importantly, all solutions should consider the optimal spectral requirements of both, conscious and unconscious photo‐reception.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7065627/
An optimal spectrum is always healthiest — for the eyes, skin, and more — and as we wisely welcome blue light during the day, we must keep its balance with other light spectrums (red light and infrared light) in mind, as well.
Naturally, sunlight is usually the best example of healthy light.