Too Much Light is Harming Our Health

Living in New York, we’ve all experienced light pollution. Whether it’s by opening a window during a late-night study session or by traveling along a busy street, we frequently encounter bright nighttime lighting.

Light pollution includes any form of man-made lighting that alters the natural brightness of the night sky and can come from a variety of sources. Although a lot of light pollution comes from the city—billboards, streetlights, and building lighting—light pollution is also found in rural areas, through natural gas flares and transportation, which make up over half of all light pollution. 

Better access to electricity and more efficient lighting have contributed to greater amounts of light pollution. Among these innovations are LEDs (light-emitting diodes)—popularized in the 2000s due to their improved energy efficiency—and are now one of the most prevalent forms of artificial lighting, making up 48 percent of all lighting. However, one characteristic that LEDs differ in from previous generations of artificial lighting—such as incandescent bulbs—is the frequency of light they emit. Light emitted by LEDs tends to be more concentrated in higher frequency (blue to violet) light in contrast to earlier generations of lighting, which emitted more low-frequency (red to orange) light.

Exposure to high-frequency light at night can be disruptive to human health in multiple ways. Firstly, it can interfere with melatonin production. Melatonin, a hormone produced by the pineal gland of the brain, plays an important role in regulating and synchronizing the circadian rhythm. Melatonin production is regulated by photosensitive retinal ganglion cells and is produced more during periods of darkness when the photosensitive cells do not detect a large presence of light. Exposure to nighttime light interferes with this mechanism, reducing the production of melatonin and disturbing the circadian rhythm. Higher-frequency light has an even more adverse effect on melatonin production, as the photosensitive retinal cells are more sensitive to higher-frequency light.

Lower levels of melatonin can impact sleep and have adverse consequences over time. Melatonin is often referred to as the sleep hormone due to its role in regulating the circadian rhythm. As a result, prolonged interference with the production of melatonin can make individuals more susceptible to developing insomnia, which can lead to complications such as increased risk for heart disease, strokes, and depression. 

Circadian rhythm disruptions can also have dangerous consequences. Systemic inflammation includes forms of inflammation generally caused by chronic inflammatory diseases and can lead to complications such as neuroinflammation and eventually neurodegeneration.

A recent study analyzed the connection between nighttime light exposure and inflammation in a group of 276 young adults. Participants were asked to record their light exposure at night using portable illuminance meters over the course of a few nights, and blood samples were collected from the participants afterward. The collected blood samples were analyzed for various markers of systemic inflammation, such as C-reactive protein.

The study found an association between high levels of light exposure at night and inflammation. One possible explanation for why light pollution is linked to greater inflammation is because exposure to light at night is atypical and may result in the production of cytokines involved in immune signaling pathways. This increased immune response can cause inflammation.

Another study observed the correlation between exposure to light pollution and deteriorating gut bacterial health in zebra finch birds. In this study, one group of zebra finches was kept in their natural light habitat—12 hours of daylight and 12 hours of darkness—for two weeks, while another group was subjected to constant dim lighting that mimics urban light pollution at night. The birds in the dim lighting were found to have altered feeding times and experienced a significant increase in body mass and subcutaneous fat deposits—fat deposits below the skin. Notably, their gut bacteria composition was significantly altered, with several, more prevalent pathogenic bacteria strains, indicating that exposure to light pollution can lead to significant loss of helpful gut bacteria.

The alteration in microbial composition can explain the weight gain experienced by the finches. The lack of regular bacterial strains reduces the ability of the finches to metabolize fat, leading to a buildup of fat deposits. This effect was compounded by more nighttime feeding behavior, likely due to the brighter night conditions. Although the results observed in finches aren’t directly transferable to humans, the study can still shed light on the potentially harmful effects of exposure to light pollution on human pathology.

There is also a potential link between light pollution and an increased risk of various forms of cancer, such as breast, lung, and colorectal cancer. While more studies are required to verify the causality, melatonin has tumor-suppressing qualities, which may explain some of the correlation observed between light pollution and cancer.

Despite our daily exposure to light pollution, there are steps we can take to reduce its harmful effects. More sun exposure during the day can help the body maintain a healthy circadian rhythm and produce more melatonin at night, so getting enough natural light during the day can help lessen the risks of nighttime exposure to light. 

Physical activity has also been linked to lower sensitivity due to inflammation from light pollution. The earlier study investigating the connection between light pollution and inflammation documented that participants who were generally more physically active had lower inflammation levels than those who were more sedentary, despite being exposed to similar amounts of light pollution. 

We take steps to regulate our exposure to more harmful, blue wavelengths of light by using warmer temperature lighting, reducing our screen time at night, and making sure to turn on the blue light filter on all our devices at night.

Finally, governments and light manufacturers can take an active role in reducing light pollution. Encouragingly, Illuminating Engineering Society, a lighting standards body, started adopting lighting standards that could reduce light pollution, such as using lower-frequency LED bulbs. Governments can also help by mandating that lighting used for industrial and commercial purposes is turned off or turned down when not in use.