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Circadian Symphony
The Influence of Light and Dark on Wellbeing
Abstract:
1. Light and dark exposure are independently crucial for regulating the body clock, improving mood, cognition, alertness, immune function, metabolism, fertility, mental health and even pain relief
2. Humans spend around 90% of our time indoors - which is not sufficiently bright during the day and too bright in the evening/night (even a well lit office is 30 times less bright than an overcast day)
3. In the morning, aim for 5-10 minutes on a sunny day and 15-20 minutes on an overcast day of sunlight into the eyes
4. In the afternoon, use as much artificial light and sunlight to trigger motivation, attention and drive. Maximising light exposure during the morning and afternoon has shown to reduce the negative impact of artificial light at night
5. In the evening, try to catch the sunset to begin ramping up melatonin and reducing cortisol to help sleep. As you transition into the evening, dim lights, turn off screens and begin implementing blue light filters
6. Keep the bedroom as dark as possible as even moderate light during sleep has shown to impact metabolic function and insulin sensitivity. If you wake during the night, avoid looking at your phone and turning on lights to get around as these aggressively impact melatonin levels and therefore disrupt the remainder of your sleep
7. If you are someone that is particularly affected by SAD (Seasonal Affective Disorder), have an irregular sleep/wake pattern or live in a climate where light is a commodity - look into buying a SAD Lamp - aim for one that has a minimum of 10,000 Lux.
Have a gander in ‘The Espresso’ section which contains insights into implementing habits one at a time, getting extrinsically motivated and counteracting the damage of all-day sitting.
The body is equipped with a circadian rhythm which is the 24 hour clock regulating processes within the body such as hunger and temperature alongside sleep.
Humans in modern societies challenge the biological clock by spending 90% of the day indoors, which is problematic because during the:
Day: we are enclosed in dim lit rooms when the sun is shining bright
Night: we are bombarded by artificial light from all angles
Cells that connect the eyes to the visual processing centres of the brain are intrinsically linked to areas of the brain influencing mood and the release of Serotonin (associated with happiness, focus and calm) and Dopamine (associated with rewards and motivation).
Viewing sunlight in the first hour of waking suppresses melatonin and increases cortisol by more than 50%. This has a positive influence on our mood, stress, alertness, immune system and metabolism throughout the day.
This early release of cortisol has an inverse relationship with cortisol levels at night time (i.e. higher cortisol after waking = lower cortisol before sleep), improving the quality of sleep.
The body is able to tell what period of the day it is by essentially looking at the ratio of blue light to red light. Here’s an idea of the colour signals your brain looks for to tell the time of day:
TIME OF DAY | LIGHT COLOUR |
|---|---|
Morning | White/Blue |
Afternoon | White/Yellow |
Evening | Red/Orange |
Night | None (Dark/Black) |
LUX
Lux is a measure of how much light is being emitted from a particular source or available in a certain space.
To drive home the difference between natural and artificial light, here’s some typical Lux readings:
Bright sunny day: 40,000 to 100,000 Lux
Cloudy day: Up to 30,000 Lux
Well lit office: 500 Lux
Its clear then that artificial light is not sufficiently strong enough to provide the same stimulus.
If you’re curious, download a free Lux meter on your phone and see what your reading is right now.
So we’ve learnt about some of the game changing benefits and the importance of sun exposure, but in case that wasn’t enough, here’s some more:
IMPROVED FERTILITY AND REPRODUCTIVE FUNCTION
A 2021 study highlights the positive impact of UVB light on the skin for fertility, reproductive health and function - in particular increasing testosterone and oestrogen levels.
In order to benefit, enjoy 20-30 minutes of sun exposure onto the skin, 2 to 3 times per week.
PAIN RELIEF
Exposure to bright light has beneficial effects on diverse brain functions, including mood, cognition and surprisingly, pain.
A study suggests that bright light therapy affects pain perception by activating neurons that inhibit pain signals.
MENTAL HEALTH
A major 2023 study out of the University of Manchester, looked at how light affects our mental health. They examined the association of day and night light exposure with risk for psychiatric disorders/episodes and self-harm in over 85,000 adults. Even after adjusting for social and demographic differences, physical activity, sleep quality and cardiometabolic health, the study found:
Greater night light exposure was associated with increased risk for major depressive disorder, anxiety disorder, PTSD, psychosis, bipolar disorder and self-harm behaviour
Independent of night light exposure, greater day light exposure was associated with reduced risk of most of the same disorders/behaviours
Avoiding light at night and seeking light during the day may be the most simple and effective, non-pharmacological means of broadly improving mental health
The Framework
MORNING
Get 5-10 minutes of sunlight, ideally 30-60 mins after waking
On an overcast day, aim for 15-20 minutes
During the Winter darkness, make your internal environment as bright as possible and then get sunlight once the sun has risen
AFTERNOON
Use bright lighting and sunlight to trigger a boost in motivation, attention and drive
Expose as much skin (as appropriate!) to sunlight for a period of 20-30 minutes, 2 to 3 times a week
Sufficient sunlight during the morning and afternoon has shown promise in reducing the negative impacts of light at late-night (from artificial sources).
EVENING
As you transition to the evening phase, begin to:
reduce blue light exposure
turning off lighting
dim screens
Catching the sun as its setting for 5-10 minutes enables the body to begin reducing cortisol levels and ramp up levels of melatonin to promote a good nights sleep
Bright light, even from the likes of a mobile phone, can powerfully impact the production of melatonin. Try:
features available on your phone (e.g. Eye Comfort Shield)
features available on your computer (e.g. Night Light)
blue light blocking glasses
During the night, if you wake, try and inhibit use of light to get around (safely). Even taking a look at your phone or turning on the bathroom light will obliterate your melatonin levels, negatively impacting your sleep
A study published in 2022 found that even a single night of exposure to moderate light during sleep can disrupt metabolic function and increase insulin sensitivity - so keep your room as dark as possible when you sleep
to keep you going
One at a Time
Why the best way to change your entire life is by not changing your entire life
Skinner’s Law
In a trough? Get back on track by leveraging pain
Frog Pose
A dead simple stretch for those that sit all day
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