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In the annals of human history, the invention of artificial lighting has been hailed as a symbol of progress, enabling increased productivity, enhanced safety, and the extension of cultural activities.1 From fire to gas lamps, and from Edison's incandescent bulb to modern LED lighting, the technology to control light has fundamentally transformed the structure of human society.3 However, behind this technological achievement lies an unforeseen cost. The modern environment, where we can be exposed to light 24 hours a day, has disrupted the natural cycle of light and darkness that humanity has evolved with over hundreds of thousands of years, creating a new form of environmental stressor: 'light pollution'.5
This report aims to provide a comprehensive analysis of the reality of light pollution, which extends beyond being a mere hindrance to astronomical observation to pose a serious threat to human biological health. It will particularly focus on establishing that light exposure during sleep is not just a simple inconvenience but a powerful factor that disrupts the body's sophisticated physiological regulation systems. Light is the most crucial external signal for orchestrating the body's circadian rhythms, but when exposed at inappropriate times, it transforms into an intruder that can dismantle this entire system.
This report will delve into the biological mechanisms by which light exposure during sleep disrupts the body's core biological clock and hormone secretion systems. Furthermore, based on the latest research, it will systematically describe how this physiological disruption increases the risk of developing a wide range of non-communicable chronic diseases, including metabolic syndrome, cardiovascular disease, neurocognitive decline, and mental health issues. Finally, it will analyze the risk levels based on the physical properties of light—its intensity and color—diagnose the primary sources of light pollution in modern society, and, based on this, propose science-based mitigation strategies and technological solutions that individuals and society can implement to reclaim a healthy sleep environment. Through this analysis, this report will clarify that light exposure during sleep is a significant public health issue that can no longer be overlooked and will argue for the necessity of re-evaluating the value of darkness for a healthier future.
To understand the wide-ranging effects of light exposure during sleep on the human body, a fundamental understanding of how light interacts with our physiological systems is necessary. The human body possesses an internal system finely tuned to the natural cycle of light and darkness, and nocturnal light acts as a dissonant chord that shatters this harmony. This section will analyze step-by-step the impact of light on the body's core biological clock, hormonal regulation, and autonomic nervous system to clearly define the mechanisms of disruption.
The human body operates according to an internal biological clock, the 'Circadian Rhythm'.6 According to a 1999 Harvard University study, this rhythm has an average cycle of 24 hours and 11 minutes and maintains itself even in an environment devoid of external stimuli.7 The central command for this sophisticated internal clock is the 'Suprachiasmatic Nucleus (SCN),' located in the hypothalamus of the brain.8 The SCN acts as the 'master clock,' orchestrating and coordinating nearly all physiological processes in the body, including the sleep-wake cycle, hormone secretion, body temperature, and blood pressure changes.6
The internal time set by the SCN must be synchronized with the external world's time, namely the 24-hour cycle of the Earth's rotation. The most crucial external signal (Zeitgeber, or "time-giver") in this synchronization process is light.10 When light enters the eyes in the morning, this information is transmitted via the optic nerve to the SCN.7 The SCN interprets this light signal as a 'wake-up call,' issuing commands to all bodily systems to commence activity, thereby 'resetting' the disarrayed biological rhythm every morning.7 Thus, light plays a pivotal role in precisely aligning our internal biological clock with the external environment through the SCN.
As night falls and light disappears, the activity of the SCN decreases, and the brain's Pineal Gland begins to secrete a hormone called 'Melatonin'.10 Known as the 'hormone of darkness,' melatonin induces drowsiness as its concentration in the blood rises, acting as a powerful signal to the body that it is time to sleep.10 The periodic secretion of melatonin is crucial for forming a stable sleep-wake cycle. For instance, newborns only begin to sleep soundly through the night after about three months of age, when their melatonin secretion rhythm is established.10
However, melatonin's role extends beyond merely inducing sleep. It is one of the body's most potent endogenous antioxidants, produced in every cell to neutralize reactive oxygen species, the main culprits of cellular aging and damage.11 It is particularly concentrated in the mitochondria, the cell's energy factories, where it serves as a key defense mechanism protecting cells from oxidative stress.13 Therefore, the normal secretion of melatonin is essential not only for sleep but also for cellular-level recovery and health maintenance.
When exposed to light during sleep, this elaborate melatonin secretion system comes to an immediate halt. This suppression process begins in the eyes and is carried out through specific neural pathways in the brain. Light information is transmitted from the retina to the SCN, and the light-activated SCN sends a signal that inhibits melatonin production in the pineal gland.8
To be more specific, at night, the reduced activity of the SCN releases the inhibition on the Paraventricular Nucleus (PVN) of the hypothalamus. This allows signals to travel down the spinal cord to the superior cervical ganglion, where the released norepinephrine stimulates beta-adrenergic receptors in the pineal gland, activating the key enzyme (N-AT) that promotes melatonin synthesis.10 However, if light enters the eyes during sleep, the SCN is reactivated, which resumes the inhibitory signal to the PVN. This inhibitory signal blocks the activation of the sympathetic nerves leading to the pineal gland, causing a sharp cessation of melatonin synthesis.10 This process is extremely sensitive and rapid; even a brief exposure to strong light in the middle of the night can cause melatonin secretion to plummet.7
The body's autonomic nervous system is divided into the 'sympathetic nervous system,' which governs activity and arousal, and the 'parasympathetic nervous system,' which is responsible for rest and recovery. During healthy sleep, the parasympathetic nervous system predominates, lowering heart rate and blood pressure and allowing the body to enter a state of deep rest and recuperation.15 However, nocturnal light exposure disrupts this natural balance.
Even when one is asleep and consciously unaware, the brain detects light, which results in the activation of the sympathetic nervous system.17 Experimental studies have shown that individuals sleeping in a moderately lit room (100 lux) have a significantly increased heart rate and decreased heart rate variability during sleep compared to those sleeping in a dimly lit room (<3 lux).16 This indicates that the body is in a state of arousal and stress, similar to a 'fight-or-flight' response, at a time when it should be resting.15
Thus, light exposure during sleep does more than simply wake you up; it triggers a cascade of physiological failures. Light stimulates the SCN to suppress melatonin secretion, leading to a dual loss: the loss of the sleep-inducing signal and the loss of a powerful antioxidant protective function. Simultaneously, light disrupts the autonomic nervous system, shifting the body from a recovery mode to a stress mode. This fundamental physiological disruption lays the groundwork for the wide range of systemic health problems discussed in the next section.
The disruption of the biological mechanisms described in Part 1 leads to specific, measurable negative health outcomes throughout the body. Nighttime light exposure is no longer considered merely a sleep disturbance but is now recognized as a significant environmental risk factor that can cause or exacerbate major chronic diseases of modern society, such as metabolic disorders, cardiovascular disease, cognitive decline, and mental health problems. This section will provide an in-depth analysis of the systemic consequences of nighttime light exposure, based on scientific evidence accumulated from laboratory studies and epidemiological surveys.
One of the most prominent areas of recent research is the link between nighttime light exposure and metabolic health. A series of studies published in the prestigious journal PNAS by a research team at Northwestern University in the United States has provided strong mechanistic evidence for this connection.15
According to their key findings, when healthy adults slept for just one night under moderate lighting (100 lux), their insulin resistance the next morning was significantly increased compared to when they slept in a completely dark environment (<3 lux).17 Insulin resistance is a condition where the function of insulin, which regulates blood sugar, is impaired, and it is a key precursor to type 2 diabetes. The researchers identified the activation of the sympathetic nervous system, induced by light, as the primary cause of this phenomenon. In other words, the body's ability to metabolize glucose is compromised as it remains in a continuous state of arousal during sleep.15
These laboratory findings are consistently supported by observational studies conducted on large populations. Women who reported being exposed to light at night, such as from a nightlight or a television left on in the bedroom, had a higher prevalence of obesity than those who did not.18 In particular, a study targeting the elderly population showed a clear positive correlation between the level of light exposure in the bedroom and the incidence of type 2 diabetes, obesity, and hypertension.15
In addition to its impact on metabolic health, nighttime light exposure places an immediate burden on the cardiovascular system. The aforementioned Northwestern University study observed that the heart rates of participants who slept in a moderately lit room remained higher throughout the night.16
This is a direct result of sympathetic nervous system activation and suggests that the heart's necessary rest and recovery processes during sleep are not being properly carried out.17 During normal sleep, heart rate and blood pressure should decrease, allowing the cardiovascular system to rest. However, light exposure interferes with this process, adding to the heart's workload throughout the night. This chronic state of nocturnal sympathetic dominance can increase the risk of developing hypertension in the long term and act as a risk factor for overall cardiovascular disease.12
The effects of nighttime light exposure also extend to brain function the following day. A study conducted by a research team at Korea University revealed that even sleeping in very dim light (10 lux), just enough to barely recognize objects, has a negative impact on brain function the next day.28
Functional brain magnetic resonance imaging (fMRI) analysis confirmed a decrease in activity, particularly in the inferior frontal gyrus, which is responsible for higher-order cognitive functions such as working memory, concentration, and emotional regulation.28 This decline in brain function leads to an increase in subjectively felt fatigue and eye discomfort the next day.31 Even if one does not wake up during sleep, the brain detects the light, leading to a deterioration in sleep quality and a fragmentation of sleep architecture, with reduced time spent in deep sleep (slow-wave sleep) and REM sleep.15 This prevents the brain from fully recovering, thereby impairing alertness and cognitive performance the following day.32
Furthermore, chronic disruption of the circadian rhythm is closely related to mood disorders. Epidemiological studies have shown that elderly individuals who sleep in bright bedrooms have a significantly higher risk of developing depression compared to those who sleep in the dark.37 This is presumed to be because the disruption of the circadian rhythm affects the neurotransmitter systems involved in mood regulation.34
The International Agency for Research on Cancer (IARC), a part of the World Health Organization (WHO), has classified factors that disrupt the circadian rhythm, such as night shift work, as 'probable carcinogens (Group 2A)'.39 One of the key pieces of evidence for this classification is the suppression of melatonin secretion due to nighttime light exposure.27
Melatonin is known to have an 'oncostatic' effect, meaning it inhibits the growth of cancer cells. Therefore, chronic nighttime light exposure that suppresses melatonin secretion can weaken the body's natural cancer defense mechanisms.38 In particular, research has reported a link to an increased risk of hormone-dependent cancers such as breast and prostate cancer.27 Additionally, since melatonin plays an important role in regulating the immune system, a deficiency in melatonin can lead to impaired immune function.40
These findings point to a crucial fact: the damage caused by light exposure during sleep proceeds 'silently,' mostly without the individual's awareness. The participants in the Northwestern University study did not feel that the light had disturbed their sleep, yet their bodies showed clear physiological stress responses such as increased heart rate, sympathetic activation, and increased insulin resistance.17 This demonstrates how dangerous the common belief that 'it's fine as long as I can sleep' is. The damage accumulates insidiously under the surface of sleep and manifests in the long term as chronic disease, which is why the threat of nighttime light exposure is severely underestimated by the public.
The impact of nighttime light exposure on the human body is not uniform across all types of light. The degree of threat varies significantly depending on the physical properties of the light, particularly its 'Intensity' and 'Color.' Understanding these two factors is essential for accurately assessing the risks of nighttime light exposure and for formulating effective response strategies. This section will analyze the effects of light intensity and color on the body's physiological systems and, based on this, compare and evaluate the risk levels of major light sources in daily life.
The human body's circadian rhythm regulation system is surprisingly sensitive to light, and it does not require daylight-like brightness to cause problems. Research findings consistently show that even very low levels of light can trigger significant physiological responses.
Notably, negative effects have been observed with as little as 10 lux of light.28 10 lux is a level of brightness at which one can barely identify objects in a room, a level easily reached by a TV screen turned on from a meter away 35 or by streetlight filtering through a gap in the blinds. Simply sleeping while exposed to such minimal light has been shown to impair cognitive function the following day.28
There is a 'dose-response relationship' between light intensity and melatonin suppression, meaning the stronger the light, the greater the melatonin suppression effect.10 The 'moderate brightness' of 100 lux used in key experimental studies is much dimmer than typical indoor daytime lighting (300-500 lux), but it can easily be produced by a single bedside stand or an uncovered lamp.15 For reference, 1 lux is equivalent to the brightness of a single candle.41
The color of light, or its wavelength, can have a far more decisive impact than its intensity. The body's circadian rhythm system is particularly sensitive to light of a specific wavelength: the short-wavelength light that appears blue to our eyes.27
Blue light, with a wavelength of approximately 446-477 nanometers (nm), has the most potent effect on suppressing melatonin secretion.27 The LED screens (smartphones, TVs, computers) and cool-white fluorescent and LED lights widely used in modern society are particularly harmful at night because they emit a large amount of this blue light.12
Conversely, long-wavelength light, such as amber, orange, and red, has a much smaller impact on melatonin suppression.16 This is why, if lighting is necessary for safety at night, it is recommended to use a dim, warm-colored light source.16
A practical measure for the color of light is 'Color Temperature,' measured in Kelvin (K). The lower the color temperature value (below 3000K), the warmer and more yellow or red the light appears, and the less it suppresses melatonin. On the other hand, the higher the color temperature value (above 5000K), the cooler and more blue the light appears, and the greater its disruptive effect on biological rhythms, making it essential to avoid at night.47
To help readers apply these theoretical concepts to their daily lives, the table below provides a comprehensive comparison and analysis of the characteristics and sleep-related risks of common light sources found in modern bedroom environments. By linking abstract scientific figures to concrete everyday items, this table offers practical assistance for readers to immediately assess their own sleep environment and identify the most urgent risk factors to address.
| Light Source | Typical Distance from User | Estimated Illuminance (Lux) | Typical Color Temperature (Kelvin) | Melatonin Suppression Risk | References |
|---|---|---|---|---|---|
| Smartphone/Tablet Screen | 30 cm | 40-60 lux | >6500K (Cool White/Blue) | Very High | 32 |
| LED Television | 3 m | 5-10 lux | >6500K (Cool White/Blue) | High | 15 |
| Bedside Stand (Cool White LED) | 1 m | 100-150 lux | 5000K-6500K | Very High | 15 |
| Bedside Stand (Warm Incandescent) | 1 m | 70-100 lux | Approx. 2700K | Medium | 47 |
| External Streetlight (through blinds) | N/A | 5-15 lux | Varies (mostly cool white) | Medium to High | 33 |
| Dim Amber/Red Night Light | Floor level | <3 lux | <2200K | Very Low | 16 |
For hundreds of thousands of years, humanity's biological systems have adapted to a predictable cycle of light and darkness. However, in just over 150 years, the proliferation of artificial lighting has completely shattered this natural rhythm. Our genes are still adapted to a Stone Age environment, yet our living conditions are filled with light that never turns off for 24 hours. This 'evolutionary mismatch' is the root of the light pollution problem facing modern society, and its threat manifests in two main forms: light that infiltrates from the external environment and light emitted from the digital devices we use ourselves.
Since humans began using fire, attempts to illuminate the night have been ongoing, but it was the invention of the gas lamp in the 19th century and the advent of Edison's commercial incandescent light bulb in 1879 that changed the nocturnal landscape of society as a whole.2 These innovations enabled 24-hour factory operations and nighttime commercial and cultural activities, fundamentally reshaping the social structure.1
Today, this progress has led to widespread light pollution (Artificial Light At Night, ALAN), characterized by the 'skyglow' phenomenon in cities and 'light trespass,' where light directly intrudes into residential areas.38 Light emitted from streetlights, outdoor billboards, and building facade lighting seeps through windows, contaminating the sleep environment. A survey conducted in six Korean cities found that approximately 20% of the surveyed locations exceeded the residential light emission standard of 10 lux.40 This level is sufficient to cause biologically significant disruption.
The most potent and personalized source of light pollution in modern society is undoubtedly digital devices. Smartphones, tablets, laptops, and e-readers are particularly harmful for several reasons. First, they are held close to the face during use, resulting in a very high intensity of light reaching the retina. Second, the LED screens of these devices, for energy efficiency, contain a large amount of short-wavelength blue light, which has the strongest melatonin-suppressing effect.27
Indeed, a study comparing a group reading a printed book with a group reading a light-emitting e-book found that the e-book users took longer to fall asleep, had suppressed melatonin secretion, a delayed circadian rhythm, and reduced alertness the next morning.32 The use of such digital devices is identified as a key factor causing melatonin suppression, delayed sleep onset, and poor sleep quality in modern people, especially adolescents.34
Although many devices offer a 'night mode' or 'blue light filter' function, their effectiveness is debated. While these features do lower the color temperature of the light, some research suggests they may not reduce the light's intensity enough to completely offset its alerting effect on the brain.44 Therefore, experts agree that the most effective strategy is to completely stop using screens before bed, rather than relying on filters.44 All these phenomena ultimately show that while humanity has technologically conquered the night, in the process, we have created an environment that clashes with our biological nature. This issue requires a shift in approach across society, from individual habit changes to urban planning, architectural design, and technological development, making it a significant public health challenge.
The risks of nighttime light exposure are not applied equally to everyone. Certain age groups or individuals with specific lifestyles are more vulnerable to light pollution due to biological and environmental factors, and the resulting health damage can be more severe. This section focuses on three particularly vulnerable groups—children and adolescents, the elderly, and shift workers—to analyze the disproportionate impact of nighttime light exposure on them.
Children and adolescents are not simply small adults. Their physiological systems, especially the system that regulates circadian rhythms, are still developing and are much more sensitive to light than those of adults.57 Studies show that when exposed to the same intensity of light, melatonin secretion in children and adolescents is suppressed more easily and to a greater extent than in adults.57
This high sensitivity can have serious consequences during the critical period of growth and development. Chronic nighttime light exposure can cause growth disorders by disrupting melatonin secretion, and there are also reports of an increased risk of myopia.40 The impact on mental health is even more concerning. The use of digital devices like smartphones before bed can delay the sleep-wake cycle in adolescents, leading to chronic sleep deprivation, which has been linked to an increased risk of depression, anxiety, low self-esteem, and even suicidal ideation.34
In old age, melatonin secretion naturally decreases, and sleep tends to become lighter and more fragmented. In this context, nighttime light exposure acts as a factor that exacerbates existing age-related sleep problems.
The link between nighttime light exposure and metabolic diseases is particularly pronounced in the elderly population. A large-scale study of adults aged 63 to 84 found that the group exposed to any form of light during sleep had a significantly higher prevalence of obesity, hypertension, and diabetes compared to the group that slept in a completely dark environment.20
A potential 'vicious cycle of vulnerability' exists here. For example, an elderly person with diabetes may need to use the restroom frequently at night, or someone with neuropathy may keep a nightlight on for safety to reduce the risk of falls. However, that very nightlight can worsen insulin resistance, thereby exacerbating the diabetes.17 In other words, an attempt to manage the symptoms of a disease can inadvertently create a negative feedback loop that worsens the underlying condition. This suggests that for the elderly, it is not enough to simply advise them to 'sleep in the dark'; specific and careful guidance is needed to minimize light exposure while ensuring safety.
Shift workers are the group that experiences the most extreme form of chronic circadian rhythm disruption in modern society. They work under bright lights at night when they are biologically programmed to sleep, and they must try to sleep during the day when they should be active.39 This lifestyle creates a severe mismatch between the body's endogenous rhythm and the external environment.
As a result, many shift workers suffer from 'Shift Work Sleep Disorder (SWSD).' The classification of shift work that disrupts the circadian rhythm as a 'Group 2A probable carcinogen' by the International Agency for Research on Cancer (IARC) starkly illustrates the severity of the risk.39 Shift workers have a 2-3 times higher risk of developing cardiovascular and cerebrovascular diseases compared to the general population, and the prevalence of metabolic syndrome, gastrointestinal disorders, and mental health problems is also significantly higher.58 For them, light management is not a matter of personal choice but an essential issue of occupational health and safety. Strategic light exposure management—using bright light to maintain alertness during night shifts and thoroughly blocking light with sunglasses and blackout curtains for daytime sleep after work—is crucial for minimizing health damage.58
The analysis so far has clearly established the multifaceted and severe threats that nighttime light exposure poses to the human body. Fortunately, unlike most other environmental pollutants, light pollution is a problem that can be largely controlled and improved through individual and societal efforts. This final section, based on the scientific principles discussed earlier, presents specific and actionable strategies for creating a healthy sleep environment and minimizing the damage from nighttime light exposure. These strategies can be approached from three dimensions: environmental control, behavioral modification, and technological solutions.
The most direct and effective strategy is to physically block light from entering the sleeping space. To block ambient light pollution from external sources such as streetlights, vehicle headlights, and neighbors' lighting, using blackout curtains or blinds is highly effective.16 If it is difficult to completely cover the windows, or when traveling, wearing a high-quality sleep mask can be an excellent alternative.61
Managing light sources inside the bedroom is also crucial. The subtle standby lights from electronic devices such as televisions, computers, digital clocks, and chargers can also disturb sleep and should be covered with black tape or completely unplugged.61 The goal is to create as close to perfect darkness as possible—an environment where you can barely tell the difference between having your eyes open or closed.
Behavioral habits in the hours leading up to bedtime are crucial in determining the quality of sleep. The most essential 'Light Hygiene' rule is to stop using all types of screens—smartphones, tablets, computers, and TVs—at least 1-2 hours before sleep.44 This is the most certain way to block exposure to the blue light that suppresses melatonin secretion at its source.
Gradually dimming and warming the overall lighting environment in the house during the evening hours is also helpful. Instead of bright fluorescent lights, using only low-intensity stand lights with a low color temperature (below 3000K) can create an 'artificial dusk' effect, signaling to the brain that bedtime is approaching and inducing the natural secretion of melatonin.47
If a nightlight is absolutely necessary for safety reasons (especially for the elderly or children), its selection should be made with care. The light should be as dim as possible, the color should be in the red or amber spectrum, which has the least impact on melatonin, and it should be installed close to the floor to avoid direct stimulation of the eyes.16
The table below systematically organizes strategies for mitigating nighttime light exposure, allowing for phased implementation based on individual circumstances and effort levels. This table serves not just as a source of information but as a practical guide to help readers check their lifestyle habits and create a concrete action plan for a healthy sleep environment.
| Strategy Type | Priority | Recommendation | Rationale / References |
|---|---|---|---|
| Behavioral | Essential | Stop using all screens (smartphones, TVs, tablets) 1-2 hours before bed. | Screens are a primary source of high-intensity, melatonin-suppressing blue light. 32 |
| Environmental | Essential | Make the bedroom completely dark. Cover all electronic lights and use blackout curtains or a sleep mask. | Even very dim light (<10 lux) can disrupt sleep architecture and impair cognitive function. 28 |
| Behavioral | Essential | If a nightlight is needed, use a dim, red/amber light installed at floor level. | Long-wavelength red/amber light has the least effect on melatonin, and floor installation minimizes direct eye exposure. 16 |
| Environmental | Optimal | Keep the overall home lighting dim and warm (below 3000K) during the evening. | Creates a 'circadian dusk' environment that signals the brain to begin melatonin production. 47 |
| Behavioral | Optimal | Get at least 30 minutes of bright light (preferably sunlight) upon waking. | Strongly anchors the circadian rhythm, helping the body respond more sensitively to darkness signals in the evening. 7 |
| Technological | Optimal | Install 'human-centric' or 'circadian rhythm' smart lighting systems. | These systems automatically adjust color temperature and intensity to mimic natural light changes throughout the day, supporting natural biological rhythms. 66 |
To bridge the gap between modern lifestyles and healthy biological rhythms, a new technological field known as 'Human-Centric Lighting (HCL)' or 'Circadian Lighting' is emerging.67
These systems use color-tunable LED technology to dynamically change the intensity and color of indoor lighting according to the time of day.57 During the day, they provide bright, blue-rich light to enhance alertness and productivity. As evening approaches, they automatically switch to dim, warm light with the blue light removed, so as not to interfere with the natural secretion of melatonin.70 Being introduced in various spaces such as offices, schools, and hospitals, human-centric lighting offers a technological solution that conforms to, rather than conflicts with, our biological needs, holding the potential to become a powerful public health tool for mitigating the harms of a 24-hour society.69
This report has comprehensively established that light exposure during sleep is not merely an inconvenience but a potent and insidious environmental threat that disrupts the body's fundamental physiological systems and increases the risk of a wide range of chronic diseases, from metabolic disorders to cardiovascular disease and mental health problems. The core causal relationship is clear: Nighttime light exposure → Circadian rhythm disruption → Melatonin suppression and sympathetic nervous system activation → Impairment of metabolic, cardiovascular, and neurological functions.
The analysis revealed that this threat occurs even at very low light intensities and is particularly exacerbated by the blue light emitted from modern digital devices. Moreover, the danger is greater because this physiological damage accumulates silently, without our awareness, while we are asleep. Vulnerable populations such as children, the elderly, and shift workers are more susceptible to these risks, making social attention and tailored countermeasures for them urgent.
However, this problem is not insurmountable. Nighttime light exposure is a modifiable risk factor that we can sufficiently manage and control through our efforts. Simple behavioral changes, such as making the bedroom a sanctuary of perfect darkness with blackout curtains and keeping screens away before bed, can make a significant difference in protecting our health. Furthermore, technological advancements like human-centric lighting present the possibility of a new living environment that is in harmony with our biological nature.
In conclusion, for those of us living in the age of artificial lighting, 'darkness' is no longer an object of fear or inefficiency. Rather, it is an essential resource that we must consciously protect and reclaim for a healthy life. Individuals must strive to bring back the darkness in their sleep environments, while public health authorities, urban planners, and technology companies must jointly recognize and work to solve the societal problem of light pollution. In a world that never stops shining, the wisest path to a healthy and vibrant tomorrow begins with intentionally embracing the dark tonight.