Can bright light suppress melatonin secretion?

The short answer is yes.

Humans are generally known to have a 24-hour circadian cycle, although the intrinsic period of the human circadian pacemaker actually averages 24.18 hours. What this means is that if we cannot entrain ourselves to the light-dark cycle, with each passing day, we would be waking up roughly 15-20 minutes later, and after 10-15 days we would be noticeably out of sync with society1.

So how exactly do our bodies detect light? This happens through specialised cells, which are found within the retina. Melanopsin containing cells are responsible for the detection of short wavelength light, and also for conveying this information to the suprachiasmatic nuclei via the retino-hypothalamic tract2.

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Retinal cells containing melanopsin are photosensitive. This means they are sensitive to, and react to light. Because cells containing melanopsin are photosensitive, they are known as intrinsically photosensitive retinal ganglion cells (ipRCGs), also known as melanopsin-containing retinal ganglion cells (mRGCs).

It is worth noting that although melanopsin cells are found in the eye, they don’t play a role in seeing the outside world. Their function is to detect what is referred to as blue light.

Before we go any further, it’s important to talk about light in more detail. Light is electromagnetic radiation that can be seen by the human eye. Light travels, and is measured in waves. The length of the waves is measured in nanometres (nm). There are different wavelengths which are divided into groups including gamma (γ) rays, x-rays, ultraviolet (UV) rays, visible light, infrared light, and radio waves. Most of these waves are invisible. Light lies on the visible spectrum of the electromagnetic spectrum:

Credit: Philip Ronan – CC BY-SA 3.0,

Light has varying wavelengths, which are in the range of 380-750 nanometres. Blue light has a wavelength of 446-477 nanometres3.

Sunlight is the largest source of blue light. Artificial sources of blue light include, TVs, laptops, tablets, e-readers, smartphones and LED lights. Melanopsin containing cells in the retina detect blue light, either from sunlight, or from artificial lighting and they send signals to the suprachiasmatic nucleus (SCN), which is sometimes referred to as the master clock of the brain. Bright indoor room light at night can cause strong melatonin suppression, and the brighter the light a person is exposed to, the greater the suppression of melatonin secretion4. This can cause you to fall asleep later, impacts on the quality of your sleep and disrupts normal circadian rhythm.

How does bright light at night affect children and teenagers?

A study from 2021 found that melatonin suppression in children, when they are exposed to bright light at night, was greater compared to adults. Also pre- to mid-pubertal individuals (9–14 years) had greater melatonin suppression by light. These findings indicate that exposure to evening light can be particularly disruptive for children5.

This looks likely to be an increasingly common problem as children are being exposed to screen-based technology from an earlier age compared to ~10 years ago. In addition, with smartphones, video games, TV screens and tablets, children are spending longer periods of time in front of screens, and more time being exposed to blue light at night. 

The implications of this for people’s sleep overall health are serious. In 2019, ANSES, the French Agency for Food, Environmental and Occupational Health & Safety published an expert assessment6. Their recommendations included limiting exposure to blue light from LED displays before bedtime and at night, especially for children and adolescents. They also advised people to use “warm white” domestic lighting and opt for indirect lighting or lighting with diffusers.

The report (link in the reference list below) also refers to the toxicity of blue light to the retina, which could over the long-term lead to permanent, partial or total loss of vision over time. Some animal studies also show that the retina is more vulnerable to phototoxic effects at night, although it is not clear if this is also applicable to humans.

The 2019 ANSES report identified susceptible populations as:

  • infants, children and adolescents
  • pregnant women, due to potential health effects on the unborn child (circadian clock disruption)
  • elderly people (effects associated with glare)
  • professionals with particularly high exposure to LED lighting
  • people with eye diseases or abnormalities (phototoxicity)
  • people with sleep disorders (circadian clock disturbance)
  • people with migraines (effects associated with temporal light modulation)

What can I do to protect my sleep from the effects of blue light at night?

  • Expose yourself to plenty of bright light during the day, as early as possible, preferably natural sunlight. This can have a beneficial impact on your mood and alertness during the day.
  • Avoid looking at bright screens for at least two hours before you go to bed, and this is especially important for children and teenagers below the age of 14.
  • If you work night shifts, or use electronic devices at night, consider wearing blue-light blocking glasses. You can also install apps that filter the blue light wavelength at night.
  • Use dim, yellow or red lights for night lights. Red light is less likely to suppress melatonin.


1. Czeisler CA, Duffy JF, Shanahan TL, Brown EN, Mitchell JF, Rimmer DW, Ronda JM, Silva EJ, Allan JS, Emens JS, Dijk DJ, Kronauer RE. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science. 1999 Jun 25;284(5423):2177-81. doi: 10.1126/science.284.5423.2177. PMID: 10381883.

2. Poletini MO, Moraes MN, Ramos BC, Jerônimo R, Castrucci AM. TRP channels: a missing bond in the entrainment mechanism of peripheral clocks throughout evolution. Temperature (Austin). 2015 Dec 30;2(4):522-34. doi: 10.1080/23328940.2015.1115803. PMID: 27227072; PMCID: PMC4843991.

3. West KE, Jablonski MR, Warfield B, Cecil KS, James M, Ayers MA, Maida J, Bowen C, Sliney DH, Rollag MD, Hanifin JP, Brainard GC. Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans. J Appl Physiol (1985). 2011 Mar;110(3):619-26. doi: 10.1152/japplphysiol.01413.2009. Epub 2010 Dec 16. PMID: 21164152.

4. Zeitzer JM, Dijk DJ, Kronauer R, Brown E, Czeisler C. Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression. J Physiol. 2000 Aug 1;526 Pt 3(Pt 3):695-702. doi: 10.1111/j.1469-7793.2000.00695.x. PMID: 10922269; PMCID: PMC2270041.

5. Chellappa SL. Individual differences in light sensitivity affect sleep and circadian rhythms. Sleep. 2021 Feb 12;44(2):zsaa214. doi: 10.1093/sleep/zsaa214. PMID: 33049062; PMCID: PMC7879412.




The articles in the Sleep Psychiatrist blog have been written by Dr Dipesh Mistry. They are for educational and informational purposes only, and should not be regarded as medical advice. Always seek advice from your sleep physician, personal physician, psychiatrist, or any other suitably qualified healthcare professional in relation to any interventions or treatment for your sleep, mental health or physical health.

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