The circadian rhythm is our ‘inner clock’ that helps manage physiological processes in the body, such as temperature regulation, cortisol, sex hormones, metabolism, digestion, immune function, alertness and sleep. Light exposure throughout the day plays an essential role in regulating the circadian rhythm and, therefore, impacts the quantity and quality of sleep.
The Effect of Light
Natural daylight exposure outside at high intensities advances the timing of sleep to earlier hours, improves sleep quality and affects the duration of sleep. It has been shown that for each additional hour spent outdoors, sleep is advanced by 30 minutes.
The story doesn’t end with improved sleep, but mood could also greatly be impacted by light exposure. Even moderate changes in the sleep-wake cycle can impact mood. Light can further directly affect mood by modulating the availability of serotonin and other neurotransmitters.
A 2023 report showed that mood and sleep-related issues could be rooted in the light exposure-related behaviors of people. Spending time outdoors improved mood in participants, showing that inadequate daytime light exposure suppressed melatonin, resulting in poor sleep quality, sleep deprivation and a circadian phase delay.
Sunlight Timing
A 2024 study looked at the associations between sleep quality and sunlight exposure. They found that the timing of sunlight exposure was the best predictor of sleep quality the next evening. It seems like morning sunlight exposure had better quality sleep as a result.
Imogen Russell, certified sleep consultant and owner of The Little Sleep Company, told the Epoch Times that “ideally, upon waking, we would be exposed to natural light sources. I always encourage my clients to open their blinds and take their tea or coffee outside to support the positive influence of light in the mornings.” She added that throughout the day, working near naturally lit windows and taking a chance to get out for fresh air can support them feeling alert and refreshed. As the day progresses, avoid blue light (especially two hours before bed) and switch to warmer tones like reds and oranges. This will be much more conducive to sleep, Russel said.
Artificial Light
Artificial light has changed many people’s exposure to light, especially during evening and night hours. This has been shown to increase the risk of developing circadian rhythm sleep-wake disorders caused by the misalignment of light-dark cycles. It is well-known that nocturnal light can alter sleep and circadian rhythm in humans.
The circadian system is most sensitive to light in the evening hours and exposure to artificial light in the evening can delay the circadian clock and therefore, sleep. Light from LED screens interferes with melatonin secretion and sleep, as well as next-morning alertness.
“Blue and white lights, which contain blue light rays, can trigger photoreceptors in the retina to send a signal that suppresses melatonin and shifts circadian rhythms. Hence, these are best avoided before sleep,” Russell said.
Light Therapy
Light exposure therapy involves exposure to bright lights, which prevents the production of melatonin and can shift a circadian rhythm. This may be useful in cases of insomnia or where a need for a gradual shift in circadian rhythm is necessary, Russell said.
Light therapy can be used as a non-invasive and effective therapeutic option with no side effects to improve general well-being, mood and sleep. It has even been shown to be effective in treating psychiatric and mood disorders. Bright light therapy is a well-recognized and effective first-line treatment for Seasonal Affective Disorder, as symptoms seem to improve after just a few days of treatment.
Light therapy is also used to treat depression as a second-line treatment, but achieving a therapeutic effect usually takes about 2-5 weeks.
Symptoms of a Circadian Rhythm Sleep-Wake Disorder
According to Russell, circadian rhythm sleep-wake disorders can cause a variety of symptoms, including:
- Difficulty falling asleep, staying asleep, or falling back asleep, unpredictable sleep-wake times, waking up earlier or later than desired, or sleeping during the day
- Excessive daytime sleepiness or decreased alertness
- Depression, irritability, stress or mood changes
- Impaired attention, cognitive ability, concentration, or short-term memory
- Headaches or digestive problems
Optimize Circadian Rhythm For Improved Sleep
Russell shared the following tips with the Epoch Times on how to optimize sleep-wake cycles:
- Increase your exposure to natural light during the day, especially during winter months
- Decrease light exposure later in the day
- Avoid screens in the 2 hours leading up to sleep
- Wake at the same time every day
- Balanced exercise and nutrition positively influence sleep
- Take any opportunity to be outside; green spaces are naturally restorative and support sleep
- Avoid caffeine and alcohol
- Optimize your sleep environment, invest in blackout blinds, control the temperature, ventilate and consider noise disruptions
- Practice gentle movement, mindfulness and journaling to offload concerns that can cause you to ruminate in bed
- Consider adding supplements to your day; deficiencies can cause sleep disturbance so ensure you have a balanced intake of nutrients. Iron and vitamin D are common deficiencies.
Medical doctor, Dr Sulagna Misra, recommends practicing waking up with the sun rising. “It’s a beautiful view and sets the day.” We also want to lower light exposure as we get closer to sleep so that we mimic nature and what is expected of our bodies to start the process of sleeping.
The bottom line is that any change in sleep needs to be evaluated immediately before it becomes a chronic problem. We spend a lot of time in our lives sleeping. “Sleep is very important and there is a reason that sleep deprivation is used as a method of torture,” she added.
Dr Dawn Ericsson, obstetrician-gynaecologist, told the Epoch Times that the typical person spends 90% of their time indoors, with much of that time engaged in screen time, thus “We must incorporate adequate daily doses of sunlight and conscientiously offset our increased exposure to artificial light. Something as small as your refrigerator light, stove light or even a tiny night light could affect the regulation of your circadian rhythm.”
She added that exposure to natural sunlight, particularly early morning light which emits more red and infrared light, helps to maintain, correct or reset a person’s circadian rhythm. “We should aim for exposure to 10-15 mins of natural sunlight before noon and a total of 15-30 mins daily”, she said.
“Natural sunlight plays a critical role in maintaining our circadian rhythm but effects many other biochemical processes such as Vitamin D production, mood balance, memory, glucose and weight regulation, blood pressure control, immune function and cellular communication. Adequate regular exposure to natural sunlight is therefore critical in optimizing wellness,” she added.
