Written by Peter and Amanda, founders of SLO Sleep.
Short answer: Yes. Light is the strongest signal your body clock gets. Ordinary room light in the evening delays melatonin, the hormone that signals night. Light while you sleep affects your body overnight too. Dim the lights in the evening and keep the bedroom dark. Where you can't control the room, wear an eye mask.
How does light affect your body clock?
Your body clock runs on a roughly 24-hour cycle. Light tells it what time it is. In the evening, darkness lets your body release melatonin, which helps signal that it's night.
The timing of light matters. The same light can push your clock earlier or later depending on when you see it. That's why light is the main tool for shifting the body clock after long-haul travel (Janse van Rensburg 2021).
Does ordinary room light really make a difference?
Yes. A lab study tested 116 healthy adults aged 18 to 30. Compared with dim light, ordinary room light in the evening delayed the start of melatonin release in almost everyone. It also shortened the melatonin night by about 90 minutes. Room light during the usual sleep hours suppressed melatonin by more than half in most trials (Gooley 2011).
What about screens before bed?
One lab study compared reading on a light-emitting eReader with reading a printed book in the hours before bed. With the eReader, people took longer to fall asleep and felt less sleepy in the evening. They had lower melatonin and a later body clock, and were less alert the next morning (Chang 2015).
Is it bad to sleep with the light on?
A lab study found that one night with the overhead room light on, compared with a dim room, raised night-time heart rate and next-morning insulin resistance in healthy young adults (Mason 2022). It's a good reason to keep the bedroom dark.
What do the experts recommend?
An expert consensus on sleep in athletes recommends a cool, dark and quiet bedroom, limiting screens and light before bed, and caution with caffeine (Walsh 2021). The 2021 jet lag consensus statement Peter co-authored lists eye masks and limiting screens as part of managing light on long trips (Janse van Rensburg 2021).
What should you change first?
| Light source | What the research found | Simple change |
|---|---|---|
| Room lights in the evening | Delayed melatonin in healthy adults (Gooley 2011) | Dim the lights in the evening, especially in the hours before bed |
| Light-emitting screens before bed | An eReader delayed sleep and the body clock (Chang 2015) | Put the screen away earlier, or lower the brightness |
| Light while you sleep | Raised night-time heart rate (Mason 2022) | Blockout curtains, cover standby lights, or an eye mask |
| Early summer sunrise | Light is the strongest signal to the body clock | Practical tip: blockout curtains or an eye mask if light is waking you early |
| Hotel rooms and planes | You can't control the light | An eye mask you bring with you |
Does an eye mask help?
A mask gives you darkness wherever you are. In hospital intensive care units, eye masks and ear plugs were linked to better self-rated sleep (Karimi 2021). One study of healthy adults suggests a week of wearing an eye mask at night may help learning and alertness (Greco 2023).
The SLO Sleep Mask is contoured, so it sits softly over your eyes without pressing on them, with an adjustable strap. It's $39, with free shipping on orders over $49 and our 30-Night Sleep Easy Promise. See how the main sleep masks in Australia compare.
Frequently asked questions
Is a night light bad for sleep?
Studies compared very dim light with ordinary room light, so keep any night light as dim as possible.
Does night mode on my phone fix the problem?
The studies here didn't test night mode. Lowering brightness and putting the phone down earlier are safer bets.
Do I need complete darkness?
The research compares room light with dim light. Getting the room dim is the main goal. A mask gets you there anywhere.
What if I still can't sleep?
We're not doctors. If you regularly can't fall asleep or stay asleep, see your GP.
References
- Gooley JJ, Chamberlain K, Smith KA, et al. Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans. J Clin Endocrinol Metab. 2011;96(3):E463-E472. doi:10.1210/jc.2010-2098
- Chang AM, Aeschbach D, Duffy JF, Czeisler CA. Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proc Natl Acad Sci U S A. 2015;112(4):1232-1237. doi:10.1073/pnas.1418490112
- Mason IC, Grimaldi D, Reid KJ, et al. Light exposure during sleep impairs cardiometabolic function. Proc Natl Acad Sci U S A. 2022;119(12):e2113290119. doi:10.1073/pnas.2113290119
- Walsh NP, Halson SL, Sargent C, et al. Sleep and the athlete: narrative review and 2021 expert consensus recommendations. Br J Sports Med. 2021;55(7):356-368. doi:10.1136/bjsports-2020-102025
- Janse van Rensburg DC, Jansen van Rensburg A, Fowler PM, et al. Managing travel fatigue and jet lag in athletes: a review and consensus statement. Sports Med. 2021;51(10):2029-2050. doi:10.1007/s40279-021-01502-0
- Karimi L, Rahimi-Bashar F, Mohammadi SM, et al. The efficacy of eye masks and earplugs interventions for sleep promotion in critically ill patients: a systematic review and meta-analysis. Front Psychiatry. 2021;12:791342. doi:10.3389/fpsyt.2021.791342
- Greco V, Bergamo D, Cuoccio P, et al. Wearing an eye mask during overnight sleep improves episodic learning and alertness. Sleep. 2023;46(3):zsac305. doi:10.1093/sleep/zsac305