What Published Studies Say About Evening Light and Sleep, Including Red Light
The short version
Light is one of the main signals the body uses to keep time. Studies in people show that room light in the evening can shift the body clock and lower melatonin. Red light has been studied far less, the studies are small, and their methods differ a lot. Findings are mixed. This article summarizes what five published papers measured. It does not tell you what any light will do for you or for anyone in particular.
Why timing matters
The body keeps a roughly 24 hour internal clock, and light reaching the eyes is one of its strongest cues. Melatonin, a hormone that rises in the evening, is a common marker researchers use to track that clock.
In a 2011 analysis in the Journal of Clinical Endocrinology & Metabolism, Gooley and colleagues looked at 116 healthy volunteers aged 18 to 30 who lived in a research center for at least five consecutive days [1]. They compared ordinary room light (under 200 lux) with dim light (under 3 lux) during the eight hours before bedtime. The authors reported that room light delayed melatonin onset in 99 percent of individuals and shortened the length of the melatonin signal by about 90 minutes. This was a retrospective analysis of data from two studies, done in a controlled research setting with young adults.
Does color matter?
Wavelength is the color of light. Researchers have asked whether red light acts on the body clock the way white or blue light does.
Figueiro and Rea (International Journal of Endocrinology, 2010) studied 12 adults aged 19 to 53 [2]. Participants stayed awake for 27 hours in a lab and received one hour exposures at 40 lux at the eye from narrowband blue light (peak 470 nm), narrowband red light (peak 625 nm), or stayed in dim light, at several times across the day and night. The authors reported that only the blue light lowered nighttime melatonin. Both colors raised nighttime cortisol compared with dim light. The paper reports a small sample, and melatonin data usable for only 7 people because the lab reported high readings only as "greater than 50 pg/ml" and the samples could not be reassayed. It used one light level and one exposure length, and pupil area, measured in 5 other people, was larger under the red light than under the blue.
This helps explain why red light is often described as less disruptive to melatonin than blue light in a lab. It does not show that red light improves sleep.
Red light studies on sleep
A small study in athletes. Zhao and colleagues (Journal of Athletic Training, 2012) studied 20 female basketball players from one team, mean age 18.6, randomly assigned to a red light group (10) or a placebo group (10) [3]. The red light group lay under a whole body device at an average of 658 nm for 30 minutes each night for 14 days, at a stated dose of 30 J/cm2. The placebo group lay under the device without light. Irradiance was not reported. Participants completed a sleep quality questionnaire, and blood was drawn at 8:00 am before and after the 14 days. After 14 days, the red light group scored better on the questionnaire (the Pittsburgh Sleep Quality Index) and had higher morning melatonin than the placebo group (38.8 versus 23.8 pg/mL). The paper has no limitations section. Features of the design that limit what can be concluded include the small number of people, one team, a short period, a self reported sleep measure, and a single morning blood draw at each time point.
Near infrared at home. Giménez and colleagues (Biology, 2023) selected 62 adults with mild sleep complaints, and 56 completed the study (ages 25 to 64) [4]. Participants sat in front of a desk lamp style module that delivered 850 nm near infrared light at 5 mW/cm2 to the face, neck and hands, from 9:30 am to 12:30 pm, five days a week for four weeks. Doses were 1, 4 or 6.5 J/cm2 against a placebo, set through pulse settings and session length. The study ran in both winter and summer. The authors reported no significant effects on sleep or circadian measures. At the highest dose, and only in the winter group, they reported changes in mood, drowsiness, a blood marker and resting heart rate. Each dose and season group had about 6 to 8 people.
Near infrared before bed. Kennedy and colleagues (Journal of Clinical Sleep Medicine, 2023) had 30 adults aged 30 to 60 with a sleep complaint wear a neck collar with LEDs at 660, 740, 810 and 870 nm, or an identical collar that gave off no light [5]. Participants used it for 25 minutes in the hour before target bedtime, every other night, for three weeks. Researchers measured sleep with a finger worn tracking ring, sleep diaries and questionnaires. The sham controlled trial found no difference between groups on the objective sleep measures. Participants who used the active collar reported better sleep, relaxation and mood, while participants who used the sham collar did not, and both groups improved on the Insomnia Severity Index. The authors described their analyses as exploratory and the study as underpowered. They also noted that the tracking ring's feedback may have changed sleep habits in both groups. The trial included mostly White women in one city and was funded by the maker of the device.
What the studies cannot tell us
- Small samples. The red and near infrared studies here had between 20 and 56 people, and the dose groups were smaller.
- Different methods. Wavelength, dose, session length, time of day, body area and sleep measures all varied, so the studies cannot be stacked into one answer.
- Self report. Several sleep outcomes were questionnaires, which can be affected by expectations.
- Specific groups. Young research volunteers, one athletic team and adults with sleep complaints do not represent everyone.
- Funding and design. One trial was funded by the device maker. One paper did not report irradiance.
- No guarantee for any device or person. Findings from a study cannot be assumed for a consumer device, a different setting or any individual.
Practical takeaways from the research
The best supported finding here is about timing of room light: researchers measured that evening room light shifts melatonin timing and shortens its duration. For red and near infrared light, the honest summary is that the evidence is limited and mixed.
If you have trouble sleeping, or you feel unusually tired during the day, talk to a clinician about sleep problems. Light devices and articles like this one are not a substitute for medical advice, and this article does not diagnose or advise on any condition.
Related reading
Several of these studies used light near the face, so our short guide on red light therapy with eyes open or closed is a useful companion.
For a plain explanation of the colors mentioned above, see red light vs near infrared vs blue light.
If you want to see how session schedules are usually described, read how often people use red light therapy.
Sources
All pages below were opened and checked on October 15, 2026.
- Gooley JJ, Chamberlain K, Smith KA, et al. J Clin Endocrinol Metab. 2011;96(3):E463 to E472. PubMed
- Figueiro MG, Rea MS. Int J Endocrinol. 2010;2010:829351. PMC
- Zhao J, Tian Y, Nie J, Xu J, Liu D. J Athl Train. 2012;47(6):673 to 678. PMC
- Giménez MC, Luxwolda M, Van Stipriaan EG, et al. Biology (Basel). 2023;12(1):60. Journal page
- Kennedy KER, Wills CCA, Holt C, Grandner MA. J Clin Sleep Med. 2023;19(9):1669 to 1675. PMC