Light plays a fundamental role in regulating our sleep-wake rhythm, a process largely influenced by two essential hormones: cortisol and melatonin. While daylight is a natural synchronizer of our internal clock, exposure to certain artificial lights, in particular blue light from screens and LEDs, can desynchronize these biological processes and alter sleep quality.
The hypothalamic-pituitary-adrenal (HPA) axis: the link between light and hormones
Our circadian cycle relies on fine coordination between the central nervous system and the endocrine system. Exposure to light acts on the hypothalamus, which sends signals to the pituitary gland to modulate cortisol production via the adrenal glands. This cortisol, often referred to as the “stress hormone”, is essential for waking up and staying awake during the day.
Blue light, particularly when perceived in the morning, strongly stimulates this HPA axis, increasing cortisol and promoting cognitive and physical activity. However, late exposure can disrupt this system by delaying the production of melatonin, the hormone that prepares the body for sleep.
Effects of blue light on sleep
Research shows that blue light has contrasting effects depending on the time of day:
- Morning: Exposure to blue light stimulates cortisol production and promotes wakefulness, improving alertness and mood.
- During the day: Its impact remains moderate, although some studies suggest that high light exposure can stabilize circadian rhythms.
- Evening: Blue light inhibits melatonin secretion, making it harder to fall asleep and disrupting sleep quality.
Special case of the elderly: Increased vulnerability
As we age, our sensitivity to light diminishes, which can lead to sleep disorders and fragmentation of sleep-wake cycles. A recent study showed that exposure to blue light in the morning improved circadian rhythm stability and reduced night-time awakenings in the elderly. Evening exposure, on the other hand, delayed sleep onset and reduced sleep quality.
Blue light filters: an effective solution?
Faced with the risks of overexposure to blue light in the evening, screen manufacturers have developed night modes that reduce the emission of this wavelength. However, a study showed that only 9.7% of users regularly activated these filters, with no significant effect on overall sleep quality. Anti-blue-light glasses, on the other hand, appear to offer more effective protection by filtering light directly at source.
What to remember?
- Morning: Exposure to intense blue light promotes wakefulness and alertness.
- Evening: Reducing exposure to blue light improves sleep quality.
- Seniors: Early morning exposure to blue light can help stabilize their sleep-wake rhythm.
- Filters: Filtering applications are not very effective, but physical solutions (glasses) offer more reliable protection.
By adapting our exposure to blue light, we can optimize our biological rhythms and improve our sleep on a daily basis.
Learn more about Lactium for stress management!
Sources:
The influence of blue light on sleep, performance and wellbeing in young adults: A systematic review.
Silvani MI, Werder R, Perret C.
Front Physiol. 2022 Aug 16;13:943108.
doi: 10.3389/fphys.2022.943108.
The bright and dark side of blue-enriched light on sleep and activity in older adults.
Barroggi Constantino D, Lederle KA, Middleton B, Revell VL, Sletten TL, Williams P, Skene DJ, van der Veen DR.
Geroscience. 2025 Jan 17.
doi: 10.1007/s11357-025-01506-y.
Efficacy of Morning Shorter Wavelength Lighting in the Visible (Blue) Range and Broad-Spectrum or Blue-Enriched Bright White Light in Regulating Sleep, Mood, and Fatigue in Traumatic Brain Injury: A Systematic Review.
Chow CM, Ekanayake K, Hackett D.
Clocks Sleep. 2024 May 28;6(2):255-266.
doi: 10.3390/clockssleep6020018.
Effects of evening smartphone use on sleep and declarative memory consolidation in male adolescents and young adults.
Höhn C, Hahn MA, Gruber G, Pletzer B, Cajochen C, Hoedlmoser K.
Brain Commun. 2024 May 17;6(3):fcae173.
doi: 10.1093/braincomms/fcae173.
Do blue light filter applications improve sleep outcomes? A study of smartphone users' sleep quality in an observational setting.
Rabiei M, Masoumi SJ, Haghani M, Nematolahi S, Rabiei R, Mortazavi SMJ.
Electromagn Biol Med. 2024 Apr 2;43(1-2):107-116.
doi: 10.1080/15368378.2024.2327432.
The Influence of Light Wavelength on Human HPA Axis Rhythms: A Systematic Review.
Robertson-Dixon I, Murphy MJ, Crewther SG, Riddell N.
Life (Basel). 2023 Sep 26;13(10):1968.
doi: 10.3390/life13101968.