Light pollution is harming our health.

September 7, 2024

Light Pollution is Harming Our Health

As the nights become increasingly bright, the list of health issues associated with artificial lighting continues to grow, encompassing everything from insomnia to cancer.

How Light Pollution Affects the Human Body

The impact of artificial lighting on health can be explained through several mechanisms. Here are the main pathways of influence:

Disruption of Sleep

Nighttime light can trigger insomnia, which itself is a risk factor for many diseases. Excessive artificial lighting disrupts our normal sleep-wake cycle, making it difficult to fall asleep or maintain good sleep quality.

Inhibition of Melatonin Secretion

Light reduces the body's ability to produce melatonin. Melatonin is a sleep hormone secreted by the pineal gland in dark conditions, possessing anti-inflammatory and tumor-suppressing properties. When we are exposed to nighttime light, melatonin secretion is inhibited, potentially increasing the risk of various diseases.

Disruption of Gut Microbiota

Artificial lighting can also disrupt the daily rhythms of gut microbiota. Gut microbiota are crucial for our overall health, and their disrupted rhythms may lead to various health issues.

Impact on Retinal Cells

The eyes perceive light through rod and cone cells in the retina, as well as a special type of neuron called intrinsically photosensitive retinal ganglion cells. These neurons are responsible for synchronizing circadian rhythms, promoting melatonin release, and communicating with neurotransmitters throughout the brain. Excessive artificial lighting may interfere with the normal functioning of these cells.

It is worth noting that individual sensitivity to light pollution can vary significantly. A study found that when participants were exposed to light levels similar to those in modern homes, their melatonin levels dropped by an average of 50%, but the sensitivity differences among individuals exceeded 50 times. This means that some people may be more susceptible to the effects of light pollution than others.

LEDs are a Major Problem

Outdoor lighting from streetlights, building security lights, illuminated billboards, and store signs seeps into homes. In more remote areas, gas flares and transportation networks illuminate the sky. In fact, according to a review of light pollution published this spring, these areas produced over 50% of the nighttime light measured by satellites.

Another key source of nighttime light is indoor lighting, particularly the bright screens of computers, tablets, smartphones, televisions, and other devices found in most homes.

Both of these light sources increasingly come from light-emitting diodes (LEDs), which were introduced in the early 21st century to reduce energy consumption. Unlike incandescent bulbs that emit long-wavelength, amber light, LEDs emit more short-wavelength blue light, which may be harmful to health.

Mario Motta, a former member of the American Medical Association's Council on Science and Public Health and a retired cardiologist, explained, "Per watt, blue light has a 10 times greater effect on melatonin suppression than red light." Notably, this council first issued warnings about light pollution over a decade ago.

The effects of excessive nighttime light are exacerbated by a lack of sufficient sunlight exposure during the day, as many people work in windowless offices or factories. John Hanifin, associate director of the Jefferson University Light Research Program and a neurologist, pointed out, "Long-term lack of the proper doses of sunlight and darkness that we as humans should experience over thousands of years of evolution can have cumulative effects."

Minority communities are particularly vulnerable, as high-wattage outdoor "glare bombs" are often placed near residences. Urban ecologist Travis Longcore from UCLA stated that in a misguided effort, these communities are illuminated brighter than white communities to deter crime. Excessive lighting "is an environmental justice issue."

This article is based on publicly available information at the time of writing. If there are any inaccuracies, readers are welcome to point them out, and we will correct them promptly.

Strong Evidence Linking Insomnia and Cancer

The most apparent impact of excessive light on health is its effect on sleep quality. In brighter rooms, people find it harder to fall asleep. This not only leads to insomnia but may also trigger a range of other health issues.

The Impact of Light Pollution on Sleep

Research shows that light pollution in the bedroom makes sleep more fragmented, thereby reducing total sleep time. This disruption of circadian rhythms not only affects sleep quality but may also trigger broader health issues.

A study of Chinese adults found that light pollution in the bedroom led to more fragmented sleep and reduced total sleep time. This study emphasized the importance of controlling bedroom lighting to improve sleep quality.

The Relationship Between Light Pollution and Inflammation

In addition to directly affecting sleep, light pollution may also trigger inflammatory responses in the body. Another study in China found that disruption of circadian rhythms could increase levels of C-reactive protein, a marker of inflammation. Additionally, levels of other inflammatory markers may also rise.

These findings suggest that long-term exposure to excessive artificial light may lead to chronic low-grade inflammation, which is considered a potential factor in many chronic diseases.

The Association Between Light Pollution and Cancer

Excessive light exposure is also associated with hormone-sensitive cancers, particularly breast, colon, and prostate cancers. Epidemiological studies indicate that people living in areas with the most severe light pollution often have higher incidence rates of these cancers.

A 2023 study found that children living in brightly lit outdoor areas in California were at greater risk of developing certain forms of childhood leukemia. The study's author, Travis Longcore, stated, "This leukemia finding adds to the growing body of epidemiological research linking cancer to the outdoor light environment in which people live, even when controlling for other factors."

However, it is important to note that not all epidemiological studies support the link between light pollution and cancer. For example, a large study conducted in the UK did not find a clear association. This may be due to variations in the degree of exposure to outdoor lighting based on bedroom location and curtain thickness.

Individual Differences

It is noteworthy that there are individual differences in sensitivity to light pollution. A study found that when participants were exposed to light levels similar to those in modern homes, their melatonin levels dropped by an average of 50%, but the sensitivity differences among individuals exceeded 50 times.

This finding highlights the complexity of light pollution's impact on health and suggests that some individuals may be more susceptible to the effects of light pollution than others. Therefore, individual differences need to be considered when formulating relevant policies and personal protective measures.

Widespread Health Impacts

In addition to insomnia and cancer, light pollution may also have broader health impacts. While some studies are smaller in scale or in preliminary stages, they raise some concerning possibilities.

Risk of Cardiovascular Disease

Some preliminary studies suggest that long-term exposure to excessive artificial light may increase the risk of heart disease. This may be related to chronic stress and inflammation caused by light pollution. However, more research is needed in this area to determine the exact mechanisms and levels of risk.

Metabolic Diseases

There are indications that light pollution may affect the body's metabolic processes, potentially increasing the risk of diabetes. This may be related to light interfering with hormonal balance in the body, particularly affecting insulin secretion and action.

Mental Health Impacts

Light pollution may also impact mental health, particularly depression. A lack of natural light-dark cycles may disrupt mood regulation, increasing the risk of depression. However, research in this area is still ongoing, and more evidence is needed to determine the exact relationship.

Ischemic Stroke

A recent study added ischemic stroke to the list of potential consequences of light pollution. This study suggested that long-term exposure to excessive nighttime light may increase the risk of stroke, possibly by affecting blood pressure regulation and vascular function.

Fertility Impacts

The impact of light pollution on fertility has also drawn researchers' attention. Studies have found that men living in areas with more outdoor light have poorer sperm quality. Similarly, pregnant women living in these areas may experience higher rates of preterm birth.

These findings emphasize that controlling light pollution is not only important for individual health but also crucial for the reproductive health of society as a whole.

Driving Safety

Overly bright streetlights not only affect health but may also pose driving hazards. Mario Motta explained that bright blue light causes pupils to constrict, while in darker conditions, pupils should dilate. "Blue light scatters much more in the eye than red light, which causes more disability glare," Motta said. According to a review article published last year in the journal Science, this makes it more difficult to identify people or objects on the road.

This finding underscores the importance of considering public safety when designing outdoor lighting, not only to provide adequate illumination but also to avoid glare and visual interference.

Overall, while some research findings are still in preliminary stages and require further validation, there is an increasing body of evidence suggesting that light pollution may have widespread and profound effects on human health. This highlights the importance of controlling light pollution, especially at night, to protect public health.

Methods to Reduce Light Pollution

As awareness of the health impacts of light pollution grows, various sectors are beginning to take action to mitigate the negative effects of excessive lighting. Here are some measures that can be taken at the community and individual levels:

Reform in the Lighting Industry

The lighting industry is finally beginning to pay attention to this issue. In 2020, the Illuminating Engineering Society joined the call for healthier outdoor lighting. This means:

Limiting blue light wavelengths
Using the minimum required lighting levels
Employing fixtures that precisely direct light

Mario Motta pointed out that previously, 4000 Kelvin (a unit of measurement for color temperature, with higher values indicating bluer light) LED bulbs were significantly more energy-efficient than 3000K bulbs, but that is no longer the case. This indicates that we can choose healthier lighting options without sacrificing energy efficiency.

However, Motta also noted that not all decision-makers have received this information. "The problem is that many lighting engineers only buy the manual once in their lifetime... their knowledge is severely outdated," Motta said. This emphasizes the importance of ongoing education and information dissemination in addressing the issue of light pollution.

Community Action

In addition to advocating for better community lighting, a review article in Science suggests that people should ensure their homes are not overly bright at night. Specific measures include:

Turning off or dimming lights in homes, porches, and yards
Using adjustable color temperature bulbs that provide full-spectrum lighting during the day and switch to amber wavelengths after dusk
Adjusting all device settings to display warmer tones at night
Downloading apps that can further reduce blue light

Travis Longcore explained, "The idea is to reduce the dose of light that most stimulates circadian rhythms as you enter your relaxation time."

Personal Protective Measures

At the individual level, there are many other ways to reduce the impact of light pollution:

Bathroom Lighting: George Brainard noted that bathroom lights are particularly bright, and turning them on at night "is likely to suppress melatonin." He recommends using night lights or newer amber kickboard lighting instead.
Blackout Curtains: Blackout curtains are essential for bedroom windows facing external light sources.
Turning Off the TV: Do not leave the TV on all night, as this is also associated with poorer sleep quality.
Sleep Masks: Some people choose to wear sleep masks, but this is not suitable for everyone.
Covering Indicator Lights: John Hanifin found that covering indicator lights on fans, TVs, air purifiers, and computers (if your bedroom doubles as a home office) is more effective. He said, "LED lights are now cheap and ubiquitous, and they have lights on everything, which can create a lot of personal light pollution." Hanifin counted seven such indicator lights in his bedroom. "I covered them all with black electrical tape."

Raising Public Awareness

A key step in addressing light pollution is raising public awareness. This includes:

Educating the public about the health risks of light pollution
Encouraging people to take action in their homes and communities
Advocating for stricter lighting regulations and standards

Policies and Regulations

Finally, addressing light pollution requires the involvement of policymakers. Possible measures include:

Developing and enforcing regulations to limit excessive lighting
Providing incentives for businesses and individuals to adopt environmentally friendly lighting
Investing in research for healthier lighting technologies

Conclusion

Light pollution is a complex issue that requires multifaceted solutions. From technological innovations in the lighting industry to community efforts and changes in individual daily habits, everyone can contribute to reducing light pollution.

As our understanding of the health impacts of light pollution deepens, the urgency to take action is also increasing. Through collective efforts, we can create a healthier, more balanced light environment that benefits not only human health but also the balance of the entire ecosystem.

Most importantly, we need to rethink our relationship with light. As experienced throughout human evolution, bright days, dim evenings, and dark nights are crucial for our physiological and psychological health. In our pursuit of progress and convenience, we also need to respect natural laws and find a balance between artificial lighting and natural light-dark cycles.

By raising awareness, taking action, and continuing research, we can mitigate the negative impacts of light pollution and create a healthier, more sustainable living environment for current and future generations.