American Scientist

THE DARKNESS MANIFESTO: On Light Pollution, Night Ecology, and the Ancient Rhythms That Sustain Life. Johan Eklöf, translated by Elizabeth DeNoma. 272 pp. Scribner, 2023. $26.00.

I was a graduate student when I first saw the Milky Way. I, along with my future husband and two friends, stared into the immensity of sparkling specks swimming in a ribbon of silk, while lying on haystacks on Favignana, an island off Sicily. My husband and his brother are from Venice, Italy, and my friend and I are from China; all of us grew up in cities on the Bortle scale greater than 7, which means we had never seen a dark sky without the glow of city lights. We remained silent for hours as we stared at the Milky Way. I blinked back tears as I looked into the stars, feeling my own insignificance, surrounded by the vastness of our universe. As urbanization continues to increase, there are more and more of us who will never see the Milky Way, who will never look to the stars to ponder our place amongst the galaxies.

Light pollution is the excessive or poor use of artificial outdoor light at night, which disrupts natural patterns of wildlife and human sleep, contributes to the increase of carbon dioxide in the atmosphere, and obscures stars in the night sky. The Darkness Manifesto is a well-researched and beautifully written book by Swedish researcher Johan Eklöf that details the effects of light pollution on animals and humans and is, ultimately, a plea for embracing darkness. As sad as the vanishing of darkness is for humans, it is mostly an emotional loss. For many other species, though, the loss is existential. For a book with darkness in the title, it is mainly about light. The pollution of the night robs us of our appreciation for light, erasing the distinctions and making our lives narrower. It is humans who love the light and who have built civilizations that fear the darkness; this trait has ultimately created a blazing planet of light pollution, affecting more than 80 percent of Earth’s populated areas.

The book starts with twilight, describing it as a transitional place for humans, who are only visitors to the night. After all, the night belongs to most of the world’s species of mammals and insects, which hunt, hide, and mate in darkness. Eklöf describes how the rhythms of these twilight animals are impacted by light pollution, from the natural chemistry of the light-emitting protein luciferin in sea fire urchin, glowworms, and fireflies, to the disrupted star compasses of migrating birds. All animals have evolved under a natural cycle of light and dark, but light pollution obscures or even obliterates that cycle, changing daily rhythmic behaviors. Light is the most important zeitgeber, or time-giver, for our body’s circadian clock, which measures each day in roughly a 24-hour cycle. In an increasingly illuminated world, the boundaries of night and day are blurred, changing activity patterns. For example, luciferin emits light, but only starting at twilight, and the star compass of birds works only under clear night skies. Because light is such a powerful environmental cue, if it continues to increase, the existence of these animals is threatened due to vanishing transitional twilight. As Eklöf masterfully spins the tale of these animals, we follow their rhythms into twilight, feeling the loss for baby turtles that wander into the city lights as they search for the sea, and for abandoned clownfish eggs that need the dark to hatch. Each story builds the tale of an ecosystem in flux with darkness as an ecological niche being disrupted by light.

Eklöf then moves his narrative from twilight animals to those that depend on darkness, as well as the many researchers who study light’s effect on darkness, using a rich foundation of historical and current scientific sources. Although the reader grasps the urgency of light pollution, the book, especially the section “Night as an Ecological Niche,” jumps from one example to the next without much organization. It would have been helpful if the examples moved in a chronological or taxa-based fashion, but we are left with numerous case studies without a summary of conclusive impacts. However, three examples illustrating the breadth of the topics covered are notable.

First, in the 1840s, Robert Hunt, a physicist, chemist, and artist, discovered that plants germinate and flower under different wavelengths of light. This type of research is foundational for all the current work on light spectra and agricultural needs. Second, founded in 1905, the Krefeld Insect Society in Germany, whose members were priests, publishers, and teachers, joined by a love for insects, sounded the alarm of a mass insect die-off. Their carefully curated collection spanning more than 100 years propelled current research on the “insect apocalypse.” As insects are attracted to light, many spinning exhaustively until death near lampposts, light pollution is likely one of the many environmental factors causing their decline. (For more discussion, see “No Simple Answers for Insect Conservation,” May–June 2019.) Third, the elegant experiments performed in the 1950s by Eleanor and Franz Sauer, followed by Stephen Emlen, demonstrated the capacity of birds to navigate by the stars. They showed that baby birds in open cup nests imprint on the stars based on Earth’s rotation, and can be disoriented by artificial light during their migratory paths. These animals are all attracted to light in a “vacuum cleaner effect,” with light as an attractant sucking them into its lure. These three examples show the breadth of the taxa covered in the book, from plants to invertebrates to vertebrate animals, and they stood out to me because of my previous research on these topics. For an uninitiated reader on the subject of light pollution, however, the diverse effects on so many organisms might be overwhelming. Organization of the section by taxa or using a single species, possibly the bat, as a common thread to link examples would have helped the reader finish the book with overarching conclusions about the effects of light pollution.

In an increasingly illuminated world, the boundaries of night and day are blurred, changing activity patterns. 

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Nothing symbolizes darkness better than bats. Eklöf is a bat researcher, and his love for this quintessential creature of the night comes across throughout the book, including examples from mythology, such as Sri Lanka’s lore of the owl as the bat’s consort, and the Chinese bat symbol of long life and happiness. Bats, experts at hunting nocturnal insects and avoiding predatory birds, use nighttime as a refuge. Using historical research into how bats can navigate without light, Eklöf writes of blindfolding and ear plugging experiments in the 1700s, showing that blindfolded bats were able to capture prey, but ear-plugged bats were not. It was not until the 1900s, with Donald Griffin’s groundbreaking work, that these early experiments were confirmed using high-frequency sounds—echolocation. In the case of increasing streetlamps, there are two losers: the moths that are attracted to the glowing lamps, spiraling until they die of exhaustion, and the light-averse bats that are pushed further into peripheral landscapes. Although Eklöf does not give exact numbers of decline, an increasing number of studies show that bat populations are declining in urban centers globally. Recent work shows that sky brightness has doubled in the last decade; if this trend were to continue, we risk the loss of darkness that so many animals depend on, including bats.

Next, the book moves from the natural world of darkness to the ills of an artificially illuminated planet as it affects both wildlife and humans. As light disrupts our internal clocks and hormone rhythms, there is an increased prevalence of stress, depression, and sleep problems. Night-shift workers have increased risk of tumor formation because light suppresses a natural nighttime peak of melatonin, a hormone essential for sleep. Another direct result of the breaking down of melatonin cycles is a lowered level of leptin, a hormone that regulates appetite. One of the many causes of obesity could be linked to dysfunction of leptin and melatonin levels affected by light pollution. In other words, we “light ourselves obese” and we “light ourselves sick.”

Light pollution is a pervasive threat to global health, to the creatures that depend on the dark, and to ecosystem services, such as those provided by pollinating insects and bats. Increasing light pollution has caused the decline of creatures that depend on darkness; some of those being essential for ecosystem function. Thousands of workers in Sichuan Province, China, currently hand-pollinate blossoms that were previously insect pollinated. Sichuan is a 9 on the Bortle scale, a region so brightly lit that it does not sleep; light pollution is one of the hypothesized causes of its native bee decline, along with pesticide use. A human worker can pollinate 10 trees per day, but a small bee colony can handle hundreds.

Similarly, a decline in bat populations in certain areas is also apparent. Bat declines because of light pollution have been reported across Southeast Asia. For instance, rice crops are being threatened by insect attacks and diseases, which are typically alleviated by bat colonies.

Despite all the negative impacts Eklöf describes, the book is ultimately optimistic. “Less is more” is a phrase that can be applied to lighting, Eklöf writes. With the invention of LEDs, lighting is more energy efficient and can also be more easily manipulated. LEDs can be directed and constrained, eliminating unwanted light scattering. Using longer wavelengths of LED light can reduce physiological and behavioral costs, eliminating the harmful blue-ish light that eats away at our health. We can mimic the natural spectrum of light by controlling intensity, retaining the convenience of artificial light while limiting its erasure of darkness. There is a rise in darkness tourism as people begin to seek out the dark, and at the forefront is legislation recently passed in France limiting how much light can be emitted to the atmosphere. Invoking philosophers from Kafka to Rousseau, Eklöf writes of the dark as our friend, of contemplation in silence when we rest our eyes, of something beyond what we can imagine in light.

The book ends with Eklöf’s own “darkness manifesto”: to be aware of, embrace, and protect the darkness. His list of actionable items can be followed by all: first to become aware of the darkness, then to avoid blue light at night and talk to those around us about the importance of darkness, and finally to influence our own environment by limiting excessive use of night light. The book does an excellent job of evoking empathy for those animals suffering the loss of night, such that by the end, the reader is appreciative of darkness and wants to protect it. By protecting darkness, we protect our own health and the well-being of our ecosystem, which contains so many creatures dependent on the distinction between night and day. Only by following our inner rhythm and letting our eyes adjust to the dark can we truly see the animals that need the dark to survive.

As diurnal animals, we need the darkness to appreciate the light; it is in darkness that conversations lengthen and silence is profound. Eklöf wonders if his children will be able to take their own children to Lake Tolken to experience shooting stars, both to witness the celestial fireworks above, and the darkness around them needed to see it. I hope that my own children will be able to see the Milky Way, to experience that glorious ribbon of light in the darkness.