Overdosing on Light: The Effect of Artificial Light on Longevity

We dreaded it. We ran away from it. Darkness still arrived all the same.

Until it didn’t.

Since the dawn of humanity, the dark of the night has been a primordial adversary of ours. This evolutionarily conserved phobia that still affects many of us today is likely rooted in our ancestors’ fear of nocturnal predators. Stars were magnificent, but they could only offer so much protection. We had to find a way to push back the void and mimic the comfort of the day.

And thus, we mastered fire over 400,000 years ago to be our first source of artificial light. The advent of this light didn’t just provide us with safety. It also inspired creativity and innovation. Indeed, some of the earliest forms of art can be traced back millennia later to Paleolithic caves, which humans illuminated using fire to carve paintings on their walls [1].

The invention continued in the sources of artificial light themselves. Fire begot oil lamps, which gave way to gaslights, then incandescent bulbs, fluorescent tubes, and finally, the Nobel Prize-winning LED that lights up the screen you’re reading from right now [2].

Through this remarkable evolution of artificial light, few could have guessed, however, that we’d reach the point where darkness is essentially banished and, from orbit, cities glow brighter than the stars.

Today, an estimated 80% of the world’s population lives under light-polluted skies [3].

For the “so what?” crowd, as with any environmental disruptor, light pollution certainly takes a toll on our health as well. You probably felt the sting of an overdose of light in the form of eye strain or headache here and there.

But is the effect much more profound and insidious that it might actually be affecting our longevity?

Does Excessive Artificial Light Influence How Long We Live?

If outdoor artificial lights can wreak such havoc on the planet, imagine what happens inside our bodies when we’re constantly exposed to the glow of digital screens. Whether for work or leisure, most of us are glued to devices that emit artificial light well into the night. As Dr. Charles Czeisler, chief of the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School, puts it:

“We are flooding the nighttime with light that was never possible before.”

To put that impact into numbers, researchers conducted a large-scale observational study involving over 88,000 participants aged 40 and above. The goal was to assess whether artificial light at night was associated with their risk of death. Each participant wore a light sensor for a full week, a duration deemed sufficient to capture individual light exposure profiles. Researchers calculated daily light doses and divided participants into percentiles. Follow-ups over the following eight years revealed a stark pattern.

Individuals in the highest exposure group (90th to 100th percentile) had a 21 to 34% higher risk of death from any cause compared to those with the lowest exposure to artificial light.

The timing of exposure mattered as well. Light between 2:30 and 3:00 a.m. was linked to the greatest increase in mortality risk. Even after adjusting for factors like socioeconomic status, age, and physical activity levels, the relationship between artificial light and death remained significant [4].

Unfortunately, artificial light doesn’t just appear to influence lifespan — it also affects healthspan, the period of life spent free from chronic disease.

The first author of the mortality study led another experiment on artificial light and diabetes risk using a similar methodology. Those in the highest light exposure group had a 53% higher risk of developing diabetes compared to those with the least exposure [5].

Other studies, relying on satellite data instead of wearable sensors, have reported correlations between outdoor artificial light and obesity [6], breast cancer [7], and heart disease [8].

While these studies are observational and can’t establish direct causality, the consistency of the results suggests artificial light is doing more harm than we might think. This idea is further supported by well-documented biological mechanisms of damage, which we’ll explore next.

How Does Artificial Light Affect Our Health?

Although it’s difficult to isolate a single mechanism behind artificial light’s impact on health, two primary (and interlinked) pathways have been elucidated: circadian rhythm disruption and sleep disturbances.

Circadian rhythms govern nearly every biological function, from hormone secretion to metabolism. These 24-hour cycles are regulated by the suprachiasmatic nucleus (SCN), a structure in the hypothalamus that responds to natural light-dark patterns [9].

Melatonin, the hormone that signals nighttime to the SCN, is particularly sensitive to artificial light. Its production naturally peaks in darkness and drops in daylight, but studies show that exposure to nighttime artificial light suppresses melatonin levels. This suppression tricks the body into thinking it’s still daytime and is linked to metabolic dysfunction, chronic stress, and increased disease risk [10].

This reflects on sleep, as excessive artificial light at night can push sleep-wake cycles out of their normal alignment with natural light exposure. This can lead to phase shifts — either a delay or an advance in sleep timing — as well as sleep fragmentation, increased daytime sleepiness, and insomnia. Poor sleep, of course, has broad consequences, from cognitive impairment to mental health disorders like depression and even metabolic disorders [11].

Emerging evidence also suggests that artificial light can impair immune function, though all studies so far have been conducted in animal models [12].

Not all sources of artificial light have the same effect. Blue-enriched light, such as the one emitted from LED screens, appears to be the most disruptive at night. Blue light has a shorter wavelength and higher energy, making it more effective at suppressing melatonin and shifting circadian rhythms [13]. Bright light intensifies this effect, while dimmer artificial light has been found to have less significant impact.

But What about….the Bright Side of Artificial Light?

So far, we’ve built quite the case for the adverse effects of artificial light. However, what we absolutely can’t do is overlook its transformative contributions to modern life, including societal and personal health.

For many, artificial light is essential for work. Night shifts may be driven by economic demands in some cases, but in critical fields like healthcare, emergency response, and transportation, they are essential to keeping society running. In these cases, bright light plays a role in maintaining alertness, improving performance, and reducing fatigue among night workers [14].

Safety is another critical factor. Artificial light improves visibility on roads, reducing traffic accidents by making pedestrians and vehicles more visible and shortening driver reaction times [15].

Beyond the road, artificial light also plays a role in fall prevention among older adults. As people age, slower gait and shorter stride length increase fall risks, especially in low-light conditions. Well-placed lighting in nursing homes has been shown to reduce nighttime falls [16].

Then, you have the emotional component. Studies support the notion that well-lit environments at night can foster a sense of security, reduce fear of crime, and promote a more positive mood [17].

Not to mention, there’s a growing body of research exploring the benefits of (controlled) light therapy, to which we previously dedicated a full article.

So How Can We Balance Things out?

Finding the right balance with artificial light starts, fittingly, with seizing the day.

The same study that linked nighttime light exposure to higher mortality rates also revealed optimistic findings. Participants who received the most daylight had a 17% to 34% lower risk of death than those who got less [4].

The highest-surviving participants in the study tended to have little to no light exposure between midnight and sunrise. Based on these patterns, researchers estimated that those who maximize daylight while minimizing artificial light at night could live up to five years longer than those on the other end of the spectrum.

Even if reducing artificial light exposure isn’t an option, getting enough daylight may offer some protection. Scientists suggest that daylight exposure can reduce the sensitivity of the circadian rhythm to artificial light at night, potentially limiting its disruptive effects [18].

This raises an intriguing question: could artificial light mimic these benefits in the day? Some researchers think so. Studies suggest that using blue light in indoor workplaces during the day may help stabilize the circadian rhythm — again, tricking the body into perceiving it as natural daylight [19]. Results show blue-enriched lighting, commercially being referred to now as “circadian lighting”, may indeed enhance workplace performance in the day [20].

Conclusion

In this age of longevity, lifestyle has become a cornerstone of health, and light exposure may soon be part of the equation.

Unlike pillars like diet and exercise, the guidance here would be far simpler. No personal experimentation or debates with carnivore versus plant-based diets needed. No endless tweaking. Your doctor might just tell you to sit in darkness for half an hour before bed. A prescription that straightforward is a rare perk.

But that same simplicity also means there’s no way to hack your way around it. Throwing on blue-light filtering glasses — something that has yet to show real benefit [21] — won’t counteract a night flooded with artificial light. As circadian biologist Prof. Sean W. Cain says:

“Unfortunately, there’s no magic bullet here. We are day-active, night-sleeping animals, and when we don’t do that, we’re acting against our physiology.”

Adjusting to darkness might take some time. But while doing so, it’s worth reflecting on how far we’ve come. For most of history, humans chased light — fire, torches, electricity — anything to push back the night.

And we…won. No more danger of predators lurking in the dark. Humans are the top predator now (unless you count AI, but that won’t need the dark to pounce anyway).

We conquered the dark so that we can finally see its beauty and appreciate its harmony with our bodies.

References

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