The circadian rhythm is our inner clock that helps manage physiological processes in the body, including 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, 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, occurring that much earlier.
The story doesn’t end with improved sleep—mood may also be impacted by light exposure. Even moderate changes in the sleep-wake cycle can impact mood. Light can directly affect mood by modulating the availability of serotonin and other neurotransmitters.
A 2023 article published in Scientific Reports, showed that mood and sleep-related issues could be rooted in light exposure-related behaviors. Spending time outdoors improved mood in participants, while inadequate daytime light exposure suppressed melatonin, resulting in poor sleep quality, sleep deprivation, increased nighttime wakening, and a circadian phase delay.
Sunlight Timing
A July
study published in Journal of Health Psychology looked at the associations between sleep quality and sunlight exposure. The researchers found that the timing of sunlight exposure was the best predictor of the participants’ sleep quality the next evening. Morning sunlight exposure may moderate circadian rhythms, thus improving sleep, the study concluded. The duration of sun exposure was not linked to the effectiveness of sleep interventions.
“Ideally, upon waking, we would be exposed to natural light sources.” Immogen Russel, certified sleep consultant and owner of The Little Sleep Company, told The Epoch Times, “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 getting fresh air can support feeling alert and refreshed. As the day progresses, avoid blue light (especially for the 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
It’s well-known that artificial light has changed many people’s exposure to light, especially during the 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, including jet lag, shift work, and irregular sleep-wake phase disorder, where there is no set pattern for sleeping and waking. It is also 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. 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,” Russel said.
Light Therapy
Light exposure therapy involves exposure to bright lights, which prevents the production of melatonin and can shift circadian rhythm. This may be useful in cases of insomnia or where a need for a gradual shift in circadian rhythm is necessary, Russel said.
Light therapy can be used as a non-invasive and effective therapeutic option with no adverse 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 two to five weeks.
Optimize Circadian Rhythm for Improved Sleep
Russel shared the following tips 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 and avoid screens in the two hours leading up to sleep.
- Wake at the same time every day.
- 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.
Dr. Dawn Ericsson, an obstetrician-gynecologist, told The Epoch Times that people typically spend 90 percent of their time indoors, and for much of that period they are 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 to 15 mins of natural sunlight before noon and a total of 15 to 30 minutes daily,” she said.
“Natural sunlight plays a critical role in maintaining our circadian rhythm [and] affects 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.”
Dr. Sulagna Misra, who specializes in integrative medicine, recommends practicing waking up as the sun rises, “It’s a beautiful view and sets the day.”
