Red Light During Sleep Reduces Sleepiness, But Not Melatonin (study summary)


Effects of red light on sleep inertia

Mariana G Figueiro, Levent Sahin, Charles Roohan, Michael Kalsher, Barbara Plitnick, and Mark S Rea

Nature and Science of Sleep
May 3, 2019


Blue light has shown a positive effect on sleep inertia.

The problem is that blue light has a side effect of suppressing melatonin.

Red light has been shown to suppress melatonin, but only when the red light dosage is very high.

Researchers sought to reduce sleep inertia through the application of red light through closed eyes.

Decreased sleep inertia would help first responders, medical residents, and overnight shift workers.


Red light delivered to sleeping subjects through closed eyelids will decrease sleep inertia upon waking.

Red light delivered to waking subjects will reduce sleep inertia, but less than overnight intervention.

Both interventions will not raise melatonin as is seen with blue light exposure.


Subjects keep sleep logs prior to the red light portion of the experiment.

They recorded sleep patterns prior to the experiment.

Subjects slept 90 minutes.

  • group one received 628 nm (red) light through closed eyes during sleep
  • group two received 631 nm (red) light after waking
  • group three did not receive any light exposure

All groups self-reported sleepiness and performed responsiveness testing tasks. Group two wore red light goggles during that testing.

Researchers measured cortisol and melatonin from subjects’ saliva.

red light goggles improve reaction times
Red light goggles improve reaction times ((source)


After waking, all subjects incrementally improved during 30 minutes responsiveness testing.

The group receiving red light during sleep had the least sleep inertia upon waking, and throughout the testing.

The group receiving red light during testing did less well, but better than the control group.

Melatonin and cortisol did not increase in any group.


Sleep inertia is a lowered response rate within the first three hours of waking.

Researchers exposed subjects to red light through closed eyelids during sleep.

The exposure did not change the subjects’ melatonin or cortisol, but it did reduce sleep inertia.



Despite the fact that one author has a sleep mask patent pending, this is a well-constructed experiment.

This study appears to have been sponsored by the Office of Naval Research (see sponsor here),  or the National Sleep Foundation (see sponsor here).

Both add credibility to the results.


Individually tailored light intervention through closed eyelids to promote circadian alignment and sleep health by Mariana G. Figueiro PhD (author of this study) was published in Volume 1, Issue 1 of Sleep Health, Mar. 2015, pp. 75-82. This study found that flashing blue light reduced melatonin onset, but flashing red light did not.

Dose parameters were derived from this study: Measuring and predicting eyelid spectral transmittance

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