Yes, it is linked with later sleep. In a 12-year Current Biology study published 15 October 2026, 156 Toba/Qom participants in northern Argentina wore sleep trackers as electricity, internet and smartphones arrived. Sleep timing shifted about 1 hour later in both rural and semi-urban communities, and rural participants lost 35 minutes of sleep within a decade.
Key takeaways
- A longitudinal study in Current Biology (15 October 2026) studied Toba/Qom communities in northern Argentina from 2012 to 2024, analyzing more than 12,000 sleep episodes recorded with wrist activity trackers from 156 participants.
- Sleep timing moved close to 1 hour later in both rural and semi-urban communities, and rural participants lost 35 minutes of sleep within a decade.
- The shifts came as electricity reached rural communities after 2016 and, later, as internet and smartphone use spread, though the authors say these factors alone cannot fully explain the change.
- In a 2011 lab study of 116 young adults, ordinary room light in the evening delayed melatonin onset in 99% of people and shortened the body’s melatonin night by about 90 minutes compared with dim light.
- The one change: dim the lights about two hours before bed, using low lamps instead of overhead lighting.
What did the 12-year Toba/Qom study find?
Sleep got later and, in rural communities, shorter as modern technology arrived. Researchers from the Universidad de San Andrés and CONICET in Argentina and the University of Washington studied Toba/Qom communities, an Indigenous people of the Gran Chaco in northern Argentina, from 2012 to 2024. The study included rural groups that got electricity only recently and semi-urban groups that had it earlier.
Participants wore wrist activity monitors (actigraphy) that log when a person falls asleep and wakes up. Across 156 participants and more than 12,000 recorded sleep episodes, the team used linear mixed-effects models to track change over time.
| What changed (2012–2024) | Result |
|---|---|
| Sleep timing, rural and semi-urban groups | about 1 hour later |
| Sleep duration, rural group | 35 minutes shorter within a decade |
| Electricity in rural communities | arrived after 2016 |
| Internet and smartphones | spread in more recent years |
The authors, led by Leandro Casiraghi and Horacio de la Iglesia, describe it as a contemporary parallel to the sleep shifts thought to have come with industrialization.
Did electricity and smartphones cause the shift?
Not on their own, according to the authors. Earlier work in these and other communities linked both electric light and smartphones with later, shorter sleep, but the team’s analyses suggest these factors cannot fully explain the delay by themselves. They describe the change as consistent with broader processes of modernization and acculturation happening at the same time.
The earlier evidence still points in the same direction:
- Electric light. In a 2015 Journal of Biological Rhythms study, the same research group compared two Toba/Qom communities with the same cultural background, one with electricity and one without. In summer, people with electricity tended to sleep about 43 minutes less; in winter, people without electricity slept about 56 minutes longer. In summer, the difference came from later bedtimes, while wake times were similar.
- Smartphones. A 2026 study in Sleep tracked 100 participants aged 12 to 49 in three Toba/Qom communities. Smartphone users fell asleep about 13 minutes later and slept about 22 minutes less than non-users, and their melatonin onset, a marker of the body clock, came about 34 minutes later.
These studies are observational: they show associations, not proof of cause.
Why does evening light push sleep later?
Light is the main signal that sets the body clock, and light after sunset tells it that the day is not over yet. Melatonin, the hormone that rises as biological night begins, is suppressed by light.
In a 2011 Journal of Clinical Endocrinology & Metabolism study, 116 healthy adults aged 18 to 30 lived in a research center for at least five days. Compared with dim light (under 3 lux), ordinary room light (under 200 lux) in the 8 hours before bedtime delayed melatonin onset in 99% of participants and shortened melatonin duration by about 90 minutes.
The reverse also works. In a 2013 Current Biology study, 8 adults spent a week in their usual electric-lit routines and then a week camping in the Colorado Rocky Mountains with only sunlight and campfires. After camping, every measured marker of their internal clock was about 2 hours earlier, and melatonin onset moved to near sunset. Later chronotypes shifted the most.
What is the one change to make?
Dim the lights about two hours before bed. You can’t undo modern life, but you can give your body clock a clearer signal that night has started.
- Pick your bedtime by counting back from your wake time, allowing about 8 hours in bed.
- Set a “lights down” time two hours earlier and add it to your plan.
- At that time, switch off bright overhead lights and use a few low, warm lamps.
- Keep the bedroom dark for sleep.
- Pair the dim evening with daylight early in the day: a walk outside after waking makes the day-night contrast stronger.
For the morning half of that contrast, see How to Fix Your Sleep Schedule: Anchor, Light, 15 Min. World Mental Health Day: Light, Rhythm and Your Mind explains why light timing matters for mood, and if you work nights, our night shift schedule guide covers light on a flipped day. Curious whether your rhythm runs early or late? Take the Body Clock Type quiz.
What are the limits of this evidence?
The 2026 study tracked real change over time, which is rare, but it is observational and followed one Indigenous people in one region. The lab and camping studies were small or short. Together they suggest bright evenings are linked with later sleep, and that a darker evening is a low-cost habit to try.
Your day on My BodyClock
The day above on My BodyClock shows a workday built around a clear day-night contrast. Sleep runs from 10:30 PM to 6:30 AM. The day starts with a walk outside, breakfast by a window and focused work, with lunch outdoors in the middle of the day. After work come a bike ride, dinner with family and music.
At 8:30 PM, a Flow block turns the lights down: overhead lights off, lamps on, the house tidied for the night. From 9 PM, a lamp-lit wind-down with a printed book and a gentle stretch leads to bed, two hours of dim light before sleep.
Swap in your own wake time and count back. Build your version in Owaves: My BodyClock on the App Store, or join the Android waitlist.
FAQ
Does artificial light at night make you sleep later?
It is linked with later sleep. In a 12-year Current Biology study of 156 Toba/Qom participants in Argentina, sleep timing moved about 1 hour later as electricity and then smartphones arrived. Lab studies show evening room light delays melatonin, the hormone that signals biological night.
How long before bed should you dim the lights?
About two hours is a practical target. In a 2011 lab study of 116 young adults, room light in the hours before bedtime delayed melatonin onset in 99% of participants compared with dim light. Low, warm lamps instead of overhead lights make the evening darker without leaving you in the dark.
Did people sleep earlier before electricity?
Studies of communities with and without electricity suggest so. In a 2015 study, Toba/Qom participants without electricity went to bed earlier and, in winter, slept about 56 minutes longer than those in a community with electricity. A 2013 camping study found that a week of only natural light moved the body clock about 2 hours earlier.
Sources
- Casiraghi LP, Spiousas I, Trebucq LL, Coldeira MF, Godoy Peirone CR, Zhang VY, Moyano MD, Golombek DA, de la Iglesia HO. Longitudinal study of Toba/Qom communities reveals delay and shortening of sleep in real time. Current Biology, 15 October 2026. doi:10.1016/j.cub.2026.09.058. https://pubmed.ncbi.nlm.nih.gov/42880258/
- Trebucq LL, Moyano MD, Coldeira MF, Golombek DA, de la Iglesia HO, Spiousas I, Casiraghi LP. Smartphone use is associated with later and shorter actigraphic sleep, and circadian clock delays in an indigenous Toba/Qom community. Sleep, June 2026. doi:10.1093/sleep/zsag039. https://pubmed.ncbi.nlm.nih.gov/41689489/
- de la Iglesia HO, Fernández-Duque E, Golombek DA, et al. Access to Electric Light Is Associated with Shorter Sleep Duration in a Traditionally Hunter-Gatherer Community. Journal of Biological Rhythms, 18 June 2015. https://pubmed.ncbi.nlm.nih.gov/26092820/
- Gooley JJ, Chamberlain K, Smith KA, et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. Journal of Clinical Endocrinology & Metabolism, 30 December 2010 (March 2011 issue). https://pubmed.ncbi.nlm.nih.gov/21193540/
- Wright KP Jr, McHill AW, Birks BR, Griffin BR, Rusterholz T, Chinoy ED. Entrainment of the human circadian clock to the natural light-dark cycle. Current Biology, 19 August 2013. https://pmc.ncbi.nlm.nih.gov/articles/PMC4020279/
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