ALAN

ALAN (Artificial Light at Night - artificial light at night) is a term referring to any artificial light during the hours of biological darkness that disrupts the circadian rhythm, suppresses melatonin, and in the long term damages health.

ALAN is a scientific acronym for the English term Artificial Light at Night, which refers to artificial light at night. It is an umbrella term for all sources of artificial light that are active during the biologically dark part of the day - that is, at a time when the human body evolutionarily expects darkness. Sources of ALAN include LED screens of smartphones, tablets, and computers, indoor LED lighting, televisions, outdoor street lighting, advertising billboards, and any other artificial light source active after sunset.

The term ALAN is used primarily in scientific and epidemiological literature, where it describes one of the main environmental factors of modern times with measurable negative effects on human health. Research on ALAN is a growing field - hundreds of studies have been added to the PubMed database in just the last five years.

Why ALAN is a problem of the modern era

For most of human evolution, biological darkness lasted from sunset to sunrise - interrupted at most by firelight and candlelight, which do not contain a significant blue spectrum. The brain could therefore rely on darkness as a reliable signal for initiating nighttime biological processes: melatonin production, a drop in body temperature, cellular repair, and immune processes.

The arrival of electric lighting and later LED technology disrupted this evolutionarily embedded system. Modern humans are exposed in the evening and night to intense light with a strong blue component (460 to 480 nm), which retinal cells (ipRGC) interpret as daylight. The result is that the brain does not recognize night - and biological processes tied to darkness are not initiated on time or at the correct intensity. [R]

Mechanism: how ALAN affects the body

The biological impact of ALAN follows a precisely documented pathway:

Artificial light at night activates melanopsin in photosensitive retinal ganglion cells (ipRGC), whose sensitivity peaks at a wavelength of 480 nm - typically present in LED light.
Activated ipRGC cells send a signal through the retinohypothalamic tract to the suprachiasmatic nucleus (SCN) - the main circadian control center of the brain.
The SCN interprets the signal as “day” and sends a command to the pineal gland (epiphysis) to stop melatonin production.
Without melatonin, the body does not enter deep sleep, cellular regeneration slows down, immunity weakens, and metabolic regulation is disrupted.
With chronic repetition, this state leads to circadian dysregulation - a chronic misalignment of biological rhythms, which science associates with a wide range of serious diseases.

Health consequences of chronic ALAN

Scientific consensus on the health consequences of ALAN has strengthened significantly in recent years. A review of current literature highlights the following key areas:

Sleep disorders
A systematic review and meta-analysis including 15 studies with thousands of participants from multiple countries confirmed that higher exposure to both outdoor and indoor ALAN is statistically significantly associated with shorter sleep duration, poorer sleep onset, and lower overall sleep efficiency. [R]

Depression and mental health
A 2024 meta-analysis including 560,219 participants found that an increase in outdoor ALAN by 1 nW/cm²/sr is associated with a 0.43 percent increase in depression risk. For indoor ALAN, an increase of 1 lux was associated with a 3.29 percent increase in depression risk. The authors emphasized that this is the first meta-analysis to systematically quantify this relationship. [R]

Metabolic disorders and type 2 diabetes
A review of studies from 2000 to 2024 documents that chronic exposure to ALAN disrupts glucose metabolism through multiple pathways: melatonin suppression, cortisol dysregulation, impaired insulin sensitivity, and changes in insulin secretion. The result is an increased risk of metabolic syndrome and type 2 diabetes. [R]

Cardiovascular diseases
Circadian dysregulation caused by ALAN interferes with the regulation of blood pressure, heart rate, and inflammatory processes. Epidemiological studies report associations between higher ALAN exposure and increased incidence of hypertension and cardiovascular events.

Oncological risk
A systematic review and meta-analysis from 2024 including 28 studies with 2.5 million participants examined the association between ALAN and multiple types of cancer. The International Agency for Research on Cancer (IARC) classifies shift work involving circadian disruption as probably carcinogenic (Group 2A). [R]

Obesity
ALAN affects not only sleep but also the timing of food intake and fat metabolism. Nighttime light promotes late-night eating, disrupts ghrelin and leptin secretion, and reduces the thermogenic capacity of adipose tissue.

Outdoor vs. indoor ALAN

Research distinguishes two main categories of exposure:

Outdoor ALAN includes light pollution from streets, advertising, and industrial lighting that penetrates bedrooms through windows. It can be measured using satellite imagery and specialized instruments. Its intensity has significantly increased in cities over recent decades with the expansion of LED public lighting.

Indoor ALAN comes from indoor lighting, screens, and household electronics. It is directly influenced by individual behavior and, according to available studies, has a stronger effect on melatonin and the circadian rhythm than outdoor ALAN — because the light source is closer to the eyes and exposure is more direct.

ALAN and light hygiene

The Mitochondriak® philosophy is based on a simple principle: the right light at the right time. In practice, this means:

Morning and daytime - maximum exposure to natural light, ideally sunlight, which provides the body with the correct signals for alertness, cortisol, and circadian clock alignment.
Evening - elimination of the blue spectrum from artificial sources. Specific tools include blue light blocking glasses, red evening bulbs without a blue component, and minimizing screen use after 9 PM.
At night - complete darkness in the bedroom. Any light, including light from an LED alarm clock, a charging phone, or street lighting through curtains, is a source of ALAN and can disrupt the sleep cycle.

Red and near-infrared light therapy (photobiomodulation) is not part of the ALAN problem - on the contrary, red and NIR light do not activate melanopsin and, when used in the evening, can actively support the production of melatonin.

Related terms

Blue light - a short-wavelength part of the light spectrum (380 to 500 nm); the most problematic component of ALAN in terms of circadian rhythm
Circadian rhythm - the body’s internal biological clock with a 24-hour cycle; ALAN is a primary cause of its disruption in modern times
Melatonin - a sleep hormone and antioxidant produced by the pineal gland and mitochondria; ALAN blocks its production
Light pollution - a synonym for excessive presence of ALAN in the environment; an environmental issue with impacts on ecosystems as well
Light hygiene - the conscious management of light exposure at different times of the day to protect the circadian rhythm
Melanopsin - a photopigment in ipRGC retinal cells sensitive to 480 nm; mediates the biological effects of ALAN
ipRGC - intrinsically photosensitive retinal ganglion cells; the primary biological receptor for the ALAN signal
SCN (suprachiasmatic nucleus) - the main circadian control center of the brain; receives light signals and is disrupted by ALAN
Social jet lag - a chronic mismatch between biological rhythms and social schedules; also caused by chronic ALAN exposure
Blue light blocking glasses - a practical tool for reducing the impact of ALAN in the evening
Red evening bulbs - lighting without a blue component; an ALAN-safe alternative for evening hours
Photobiomodulation - therapy using red and NIR light; neutral with respect to melanopsin and suitable even in the evening

Frequently asked questions about ALAN

What does the acronym ALAN mean?

ALAN stands for the term Artificial Light at Night. In scientific literature, it refers to any artificial light source active during the hours of biological darkness - from phone screens and household LED lighting to outdoor street lamps that penetrate bedroom windows.

Why is ALAN harmful?

ALAN sends a false “daytime” signal to the brain at a time when the body should perceive darkness. Through specialized retinal cells (ipRGC), it activates melanopsin, which suppresses melatonin production and keeps the SCN - the main circadian control center of the brain - in daytime mode. The result is chronically disrupted sleep, weakened immunity, metabolic disorders, and a wide range of other health consequences documented by hundreds of studies.

Which type of light is the most problematic?

From a biological perspective, the most problematic light is that with a strong blue component in the 460 to 480 nm range. This is where the peak sensitivity of the photopigment melanopsin lies. White LED bulbs and LED screens emit significant intensity in this range. Red and orange light (above 600 nm) does not activate melanopsin and is biologically neutral in terms of ALAN.

How much light is enough to disrupt melatonin?

The threshold is surprisingly low. Research shows that just a few lux of blue light in the evening can measurably suppress melatonin secretion. For comparison - typical indoor lighting reaches 150 to 500 lux, and a smartphone in a dark room emits tens of lux directly into the eyes. Short-wavelength light disrupts melatonin even at lower intensities than longer wavelengths.

Is dark mode on a phone enough to protect against ALAN?

Dark mode reduces the overall brightness of the screen, but does not change its spectral composition - meaning it still emits blue wavelengths, only at a lower intensity. Similarly, features like Night Shift and Night Mode slightly shift the color tone toward warmer shades, but do not fully block the blue spectrum. For true melatonin protection in the evening, glasses with amber or red lenses are required, as they block 90 to 100 percent of the blue spectrum.

Does ALAN affect people who sleep only with outdoor light coming through the window?

Yes. Outdoor ALAN from street lighting penetrates through curtains and windows and can disrupt sleep even when indoor lighting is turned off. Epidemiological studies have found associations between higher levels of outdoor ALAN in residential environments and shorter sleep duration, lower sleep efficiency, and a higher prevalence of depression. Solutions include blackout curtains or a sleep mask.

Does ALAN affect children as well?

Yes, and more significantly than adults. A child’s eye lens is more transparent and allows a greater proportion of blue light to reach the retina. Children are also in a phase of intensive development, during which proper regulation of sleep and hormonal rhythms is especially critical. Exposure to ALAN in childhood is associated with delayed sleep onset, shorter sleep duration, and attention disorders.

Summary

ALAN (Artificial light at night) is one of the main environmental stressors of modern times, which, through activation of melanopsin in ipRGC retinal cells, disrupts the circadian rhythm, suppresses melatonin, and contributes to a wide range of chronic diseases. Epidemiological research links it to sleep disorders, depression, metabolic disorders, obesity, cardiovascular diseases, and increased oncological risk. The solution is not rejecting technology, but conscious light hygiene: sunlight in the morning, elimination of the blue spectrum in the evening using glasses, red bulbs, and darkness in the bedroom.

Learn more about the impact of light on health in the article How artificial blue light (ALAN) worsens quality of life, or explore our solutions for better sleep.

Scientific studies and sources

Cho Y et al. Effects of artificial light at night on human health: A literature review. Chronobiol Int. 2015. PubMed PMID: 26375320
Chen M et al. Artificial light at night and risk of depression: systematic review and meta-analysis, 560,219 participants. Environ Health Prev Med. 2024. PMC11701095
Baek JH et al. Artificial light at night and type 2 diabetes mellitus. Diabetes Metab J. 2024. PubMed PMID: 39313230
Palomar-Cros A et al. Indoor and outdoor ALAN and cancer risk: systematic review and meta-analysis, 2.5 million participants. Sci Total Environ. 2024. PubMed PMID: 39437923
Systematic review of ALAN and sleep disorders — 15 studies, updated 2025. Environment International. 2026. doi.org/10.1016/j.envint.2026