Sleep and Light Exposure: How to Manage Light to Optimize Sleep
Light exposure significantly regulates sleep by controlling circadian rhythm and melatonin production. Blue light stimulates wakefulness and red light supports relaxation. Strategic light management throughout the day—bright blue light in mornings, yellow at midday, and red light in evenings—optimizes the sleep-wake cycle. Complete darkness remains ideal for deep and restorative sleep.
Does light exposure affect sleep?
Light profoundly impacts sleep by regulating the circadian rhythm. This cyclical internal clock controls the sleep-wake cycle. Exposure to light, particularly stimulatory light of shorter wavelengths like blue light, stimulates photosensitive receptors in the brain. These signals travel to a part of the hypothalamus called the suprachiasmatic nucleus (SCN), which governs the internal clock, working like a 24-hour pacemaker. (1) (2)
Closely mimicking natural sunlight exposure—so higher exposure in the morning and throughout the day, and lower as the night approaches—is one of the best ways to optimize for sleep, even when done in-room using artificial dimmable light. (3) (4) (5)
The timing, intensity, and duration of light exposure are crucial. Early morning light anchors the circadian rhythm, while reducing light exposure before bedtime supports melatonin production and improves sleep.
Does light exposure affect sleep?
Yes, light exposure significantly affects sleep by influencing the circadian rhythm. Bright light, particularly blue light, suppresses melatonin production, promoting wakefulness. In contrast, exposure to dim, warm, or red light in the evening supports melatonin production, aiding relaxation and sleep.
Does sleeping with the lights on affect you?
Yes, sleeping with lights on can negatively affect sleep quality. Even dim light exposure at night suppresses melatonin, fragmenting sleep cycles, and reducing restorative deep sleep, which leads to fatigue and lower cognitive performance the next day.
Is it OK to sleep with a little light?
If the goal is optimizing sleep to achieve a score of 90-100%, no. Complete darkness is recommended for the most restorative night’s sleep and highest melatonin secretion. However, less light is better than more light. So if light is necessary, the warmer (orange) and longer (red) the tone, the better.
Melatonin and Circadian Rhythm
The key hormone that regulates the circadian rhythm, the body’s internal clock, is melatonin. So-called the hormone of darkness, it’s produced by the pineal gland in preparation for sleep. (6)
The environment communicates the optimal time to sleep and wake up to the brain and body via light. Light exposure has a significant impact on melatonin, with high-intensity light suppressing its secretion.
Beyond controlling the sleep-wake cycle, melatonin has numerous functions. It is an important hormone with potent anti-inflammatory effects, playing a role in anti-aging, cardiovascular health, and metabolic function. (7) (8) (9) (10) (11)
Does melatonin affect the circadian rhythm?
Yes, melatonin, so-called the hormone of darkness, dictates the sleep-wake cycle. Low light stimulates its production while high-intensity light suppresses it. To align the body’s physiology with the natural rhythm of the sun, one should use more light exposure in the morning (stimulatory) and less or longer wavelength (red, infrared) toward the evening. Supplementing melatonin can help reset the circadian rhythm in cases of jet lag or shift work.
How much melatonin to reset circadian rhythm?
Most studies show the effective dose of melatonin for improving sleep in humans to be in the range of 0.3 – 5 mg.
Lower-doses (0.1-0.3 mg/d) produce near physiological melatonin concentrations, used for internal clock synchronization, while higher doses 0.6 – 5 mg are generally used for sleep disorders. (12)
Do night lights affect melatonin?
Yes, night lights can affect melatonin production. Even low levels of light, especially blue or white light, can suppress melatonin and interfere with sleep quality. To avoid disrupting sleep, it’s better to use dim, warm-toned lights, such as red light, if a nightlight is necessary. Additionally, wearing blue-blocking glasses can be a great way to reduce exposure as well.
Light Shift: Morning to Evening
Light can dictate circadian rhythm which regulates everything from energy, metabolism, focus, and sleep. This makes it a powerful tool, which when strategically used can improve numerous areas of physical and mental performance.
In the earlier hours of the day, getting sunlight or even artificial blue light will promote wakefulness and alertness. Morning light anchors the circadian rhythm, setting the stage for focus and productivity.
As the day progresses, the light spectrum and intensity should shift towards longer wavelengths, like yellow and orange tones. Just as the sun changes its intensity when it sets, aligning such lighting with one’s internal clock works best. This shift minimizes brain arousal and melatonin suppression, setting a stage for a restful evening.
By night, limiting blue light exposure and instead, relying on red or infrared light further de-stimulates the brain and the nervous system. Just as when the sun sets, red tones dominate, so they should at night time, allowing the body to foster a deeper, more restorative sleep.
Blue Light in the Morning
Morning light exposure is a very important step to optimizing nighttime’s rest. In a way, the body needs to properly wake up, to be able to fall asleep and rest.
Blue light ranges about 400-500 nm in length, being emitted by the sun and most LED devices. (13)
Exposure to blue light or sunlight in the morning is critical to kickstarting the internal clock and promoting wakefulness. This wavelength of light, naturally abundant in sunlight, signals the brain to suppress melatonin production and increase cortisol levels, enhancing alertness and focus.
The data shows morning light can improve cognitive performance, memory consolidation, and reaction times due to the stimulation of the noradrenergic system (stress-hormones). (14) (15) (16) (17)
Morning light may also help people with insomnia, by improving daytime sleepiness and circadian signalling. Three sleep tests (ESS, PSQI, SI) improved, with one being significant, without alterations in cortisol and clock gene expression. (18)
Some individuals that wake up earlier than the sun rises use techniques like blue-light emitting glasses or a lighting system (lamp) that mimics higher intensity light spectrum, similar to the sun.
Yellow Light at Midday
Midday light exposure naturally shifts toward yellow and orange tones as the sun rises higher in the sky. Such warmer tones are in-between blue light and red light in terms of length and stimulation effect. They can help sustain alertness, focus, and productivity, without being too intense.
Shifting one’s phone to night-mode, which is thought to be less stimulating, although not blue-light free, is a great example of using warmer tones to de-stimulate. To reduce melatonin suppression, decreasing display brightness is a necessary step. (19)
Yellow light is about 570-590 nm long. It has been used in phototherapy for things like photoaging, skin regeneration, wound healing, or dermatitis, showing promising potential. (20)
Incorporating midday light exposure into one’s routine enhances energy and may reduce the afternoon slump. Even a short outdoor break or a workspace near natural light can make a difference.
Using dimmable lights with warmer tones as the evening approaches can complement the midday atmosphere, providing balance and supporting the body’s natural energy cycle.
Red Light at Nighttime
As the day transitions to evening, longer wavelengths of light like red or infrared light are preferred for relaxation. Red light has minimal impact on melatonin, allowing the brain to de-stress.
Red light (620-750 nm) and infrared light (750-1000 nm) are less stimulatory, and can penetrate deeper into skin tissue. However, the potential skin benefits are associated to intentional use of red light therapy, including red light panels or infrared sauna. Potential benefits include neural stimulation, lower inflammation, skin regeneration, wound-healing, muscle recovery, and anti-aging. (21) (22) (RLT ova, 6-14) (23) (24) (25) (26)
Switching to red light tones is generally done for the purposes of reducing stimulation from blue light. The color tone of the light does not determine its wavelength. If a light is red, it’s not necessarily red in wavelength. This brings forth the importance of effectively switching the light systems to actual red or infrared tones, which requires:
- Red light glasses – high-quality glasses, optometry-grade, tested to block shorter light spectrums than red.
- Red light bulbs – using bulbs specifically designed to emit light in the red spectrum, not just a bulb with a red coating.
- Red light panels – specific devices like red light therapy panels with LEDs engineered to emit pure red wavelength.
Does morning light increase cortisol?
Yes, exposure to morning light helps stimulate the production of cortisol, a stress hormone that plays a key role in waking the body up and promoting alertness. The bright light signals the brain to suppress melatonin and activate cortisol, which helps you feel awake and energized.
How much morning light for circadian rhythm?
For optimal circadian rhythm regulation, it is recommended to get at least 20–30 minutes of natural light exposure in the morning. Morning light, especially blue light in the range of 400-500 nm, is effective in resetting the circadian rhythm and promoting wakefulness.
In places with harsh and intense light, it is recommended to stay away from the sun, particularly during the most intense parts of the day, and use protection like UV sunscreen, UV protective clothing or umbrella, and UV sunglasses.
What time does cortisol peak in the morning?
It depends on the time of waking, circadian rhythm, stimulants, and light exposure. Typically cortisol is elevated in early mornings, within 30-60 minutes of waking up, known as cortisol awakening response (CAR). In the morning, cortisol increases, powering focus, alertness, and productivity with a slow decline as the evening approaches.
Is low cortisol in the morning high cortisol at night?
Not necessarily. The body’s cortisol levels follow a natural daily rhythm, with cortisol being high in the morning and low at night. Disruptions to this rhythm, such as chronic stress or irregular sleep patterns, can lead to abnormal cortisol levels, such as higher levels at night, which can interfere with sleep.
Typically, it’s recommended to get light exposure in the morning to naturally elevate cortisol levels which allow for better circadian rhythm signalling, leading to a healthier decline later in the day.
Is red light good for sleeping?
Red light is considered good for sleeping because it has minimal impact on melatonin production. Unlike blue or white light, which can suppress melatonin and interfere with sleep, red light is not as brain-stimulatory, thus preventing arousal at night.
What color light is best for sleeping?
Red light is considered good for sleeping because it has minimal impact on melatonin production. Unlike blue or white light, which can suppress melatonin and interfere with sleep, red light is not as brain-stimulatory, thus preventing arousal at night.
What color light is best for sleeping?
During sleep, complete darkness. 1-2 hours before sleep, low intensity and longer wavelength like red or infrared light are preferred, being less stimulatory. The warmer the tone, the gentler the light on the brain and the eyes.
Do red light glasses help with sleep?
Yes, red light-blocking glasses can help improve sleep by blocking exposure to shorter wavelength lights like blue, green, and yellow light, which can interfere with melatonin production and disrupt sleep. These glasses may be particularly helpful when using electronic devices in the evening or before bed.
Hacking Light for Sleep
Optimizing light exposure throughout the day is one of the most practical tools to enhance sleep depth and quality.
Morning
Beginning the day with natural sunlight or exposure to artificial blue light to kickstart the internal clock, boost cortisol, and elevate alertness. For those up before sunrise, blue-light emitting glasses or lighting systems that mimic sunlight can provide similar benefits.
Midday
Incorporating natural or artificial light synced with the sun’s frequency of yellow-to-orange tones. Not too intense and overpowering, but still provides sufficient light to support energy and productivity.
Evening
As 8-9 pm approaches, switching to real infrared light bulbs or red light panels as the main light source is less sleep-disruptive. Reducing brightness on devices, wearing blue-light blockers, and reducing device usage are key steps to a better sleep.
Tools like blue light filters and circadian lighting, combined with good sleep hygiene, help minimize the adverse effects of artificial light. This emphasizes the importance of aligning lighting with natural rhythms for better health.
