Light therapy: how does it work and what does the science say?

Light therapy is a science-based treatment that is gaining increasing recognition for addressing psychological and sleep-related disorders. In this article, we dive deep into the workings, applications and scientific basis of light therapy.

What is the impact of light therapy on sleep?

Light therapy affects our biological clock through exposure to specially designed light sources. This artificial light, usually bright white-blue with an intensity of about 10,000 lux, inhibits the production of melatonin in the morning—the hormone that makes you sleepy—and thus resets your biological clock. Light also plays a role in regulating your mood. Australian researchers observed in 101 healthy men that the brain produced less serotonin in winter, and more as there were more hours of sunshine that day (Lambert et al., 2002). This is a correlation in healthy men, not yet proof that light therapy works this way for everyone. Resetting your sleep-wake rhythm can, however, lead to improvements in mood, energy, and sleep quality. The light comes from light glasses or a lightbox that you can place on a table.

Light therapy works through connections between the retina in the eye and specific areas of the brain. Ordinary indoor lighting is not sufficient for this purpose: a standard table lamp provides only 300 lux, while office lighting is around 500 lux according to European standards (NBN-EN 12464-1). That is why specialized lamps or light-emitting glasses are used to achieve the desired therapeutic effect.

When is light therapy most effective?

One of the most well-known uses of light therapy is for seasonal affective disorder (SAD for short), also known as winter depression.

How common is winter depression? A recent global analysis of 24 studies with a total of nearly 33,000 participants found that about 5% suffer from winter depression, and another 9% experience a milder winter dip. The further you live from the equator, the more common it is (Kim et al., 2025). The figures vary significantly by country and measurement method: an overview of twenty studies found estimates ranging from 0 to nearly 10% (Magnusson, 2000). A winter dip is therefore much more common than actual winter depression. Winter depression is characterized by depressive symptoms such as fatigue, gloominess, and an increased need for sleep during the dark winter months.

The cause lies in a lack of natural daylight, leading to a hormonal imbalance: less serotonin and more melatonin. Light therapy helps restore this balance and is considered a standard treatment for SAD. In the Canadian CAN-SAD study, light therapy for winter depression worked just as well as the antidepressant fluoxetine (Lam et al., 2006). The side effects of light therapy are usually mild and temporary, such as headaches or eye strain. Many users report an improvement in their mood and energy levels within just a few days.

As you live closer to the equator, the chance of winter depression decreases. The closer to the poles, the greater the chance of SAD.

Light therapy can also provide relief if you have been diagnosed with Delayed Sleep Phase Disorder (DSPD), or in other words, when your sleep phases have shifted.

And what about night shifts? Here, the picture is less rosy than is often claimed. In two Dutch studies, night workers wore light glasses during their shifts: 23 nurses in a hospital (Aarts et al., 2020) and 86 security guards (Helmhout et al., 2022). In neither study were they less sleepy or less fatigued than without glasses or with placebo glasses. If you work in shifts, you benefit more from a solid light and dark plan: plenty of bright light in the first half of the night, and conversely, wearing sunglasses on the way home after your shift and using a completely darkened bedroom.

	Morning person	Night Owl
Challenge	Tired too early in the evening	Not being able to get out of bed in the morning
Light Therapy Moment	Afternoon or early evening	Immediately after waking up
Daylight Saving Time Tip	Adjust the time by about 15 minutes two days in advance.	Start the week before with about 10 minutes a day
Winter Time Tip	Extend the day; start 15 minutes a day in advance	Maintain a regular routine; stick to your bedtime

Does light therapy help with other conditions?

Although light therapy is best known as a treatment for winter depression, research has shown that it can be effective for other conditions as well:

• Non-seasonal depression: Although the evidence here is more limited, light therapy is sometimes considered when medication is ineffective or has unwanted side effects.
• Bipolar disorder: Studies show that light therapy can help bipolar depression without increasing the risk of (hypo)mania. It is considered a third-line treatment option.
• Sleep disorders: Light therapy can help with issues such as shift work disorder, jet lag, and delayed sleep phase syndrome.
• Parkinson’s disease: Sleep problems and daytime sleepiness are very common in Parkinson’s. In a small randomized study by Radboudumc, 30 people with Parkinson’s wore light glasses with blue light or placebo glasses with red lenses without light for one hour, twice a day, for two weeks. Those who received blue light reported better sleep according to their own questionnaires and were less sleepy during the day: the proportion with significant sleepiness dropped from 50% to 7% (Śmiłowska et al., 2026). After two weeks, the difference with the placebo group was not yet significant, but three weeks later it was. It is promising, but it remains a small study: participants could potentially tell which glasses they had by the color of the lenses, and sleep was only measured using questionnaires. The study used ProPeaq light glasses, which the manufacturer provided free of charge. According to the researchers, the manufacturer had no role in the design or analysis. Do you have Parkinson’s and suffer from poor sleep? Then discuss light therapy with your neurologist first.
• ADHD-related sleep problems: In children with ADHD, sleep problems are often exacerbated by medication or behavioral symptoms. Research suggests that light therapy may help improve sleep quality and possibly even reduce ADHD symptoms.
• Dermatological conditions: Dermatologists have been successfully using light therapy for several decades as a treatment method for a variety of skin conditions such as psoriasis, eczema, vitiligo, and uremic pruritus. Interestingly, light therapy originated in dermatology: the Danish physician Niels Ryberg Finsen received the Nobel Prize in Medicine in 1903 for his light treatment of skin tuberculosis.

How do you use light glasses?

We would like to give you some practical tips for using light therapy when you experience a winter dip and too little daylight makes you dejected or when you have jet lag. These tips will also benefit elderly people who have more difficulty getting moving and therefore do not get outside often enough or people who work in a moderately lit work environment:

• Use light glasses or a lamp for 30 minutes immediately after waking up to activate your biological clock (if you’re a night owl) or in the late afternoon (if you’re a morning person).
• For activities later in the evening, for that day, additional use around 4 p.m. may be helpful.
• Possibly combine morning light with the use of orange glasses that block bright light in the evening to stimulate melatonin production in the evening.

In clinical settings, a structured protocol is usually followed, for example, 45 minutes of light therapy daily for one week, often in a psychiatric outpatient clinic.

Light glasses emit much less light than a 10,000 lux lamp. This is possible because they primarily use blue light, around 460 to 480 nanometers: that is what your biological clock is most sensitive to. This way, a small light source close to your eyes can still have an effect (Śmiłowska et al., 2026).

Using a daylight lamp

• Use the lamp for 20 to 30 minutes per day (at 10,000 lux; use less powerful lamps for longer, following the instructions).
• Preferably do this early in the morning.
• Do not use the lamp after sunset; otherwise, your sleep rhythm will shift in the wrong direction.

Sleep coach Jürgen: “I use light therapy myself during the dark months and find that it helps me. But my experience doesn’t apply to everyone. Are you unsure if it’s useful for you? Then consult with your doctor or a sleep specialist.”

If you have a delayed sleep phase disorder, always consult with your treating sleep specialist. But in that case, it’s quite possible that light-emitting glasses might be used in the evening to influence your sleep rhythm.

If you work alternating day and night shifts, know when it’s best to dim the lights or turn them up. Don’t wear light-blocking glasses in the morning if you want to go to sleep after a night shift. On the contrary, avoid bright light; wear sunglasses or orange filter glasses to block it out. If you want to stay more alert during a night shift, ensure there is plenty of bright light at your workplace during the first half of the night. Light glasses can be a supplement to this, but the evidence that they truly help with night work is weak (see above). There are products on the market connected to an app; this app guides you and indicates the best time to start light therapy and for how long.

Daylight: the best light therapy

The best light therapy is free: going outside. On a sunny day, you get about 100,000 lux of light outdoors, and even on a gray day, it is still many times brighter outside than inside (300 to 500 lux).

Preferably go outside in the morning. The earlier in the day you get daylight, the better your biological clock sets itself and the easier you fall asleep in the evening. If possible, choose a walk in nature: movement, fresh air, and nature are also relaxing.

• Place your desk or favorite chair close to the window.
• Ensure good indoor lighting during the day.
• Dim the lights 2 to 3 hours before bedtime so your body can produce melatonin.

Is light therapy healthy for everyone?

Let’s start at the beginning, because, as we mentioned earlier, the cause lies in the lack of natural daylight. You might also ask: Does everyone need light therapy with light-emitting glasses or extra lamps? No, they don’t! Just make sure to get plenty of daylight during the day—it doesn’t have to be sunny to get plenty of daylight. The best form of light therapy is to go outside more often during the day. And if that isn’t enough, you should definitely consider using additional aids.

Although light therapy is promising when applied correctly, there are some limitations:

• Evidence for non-seasonal depression and ADHD-related applications is still developing.
• Some conditions continue to require additional research to further substantiate effectiveness.

Still, light therapy certainly offers a safe option for many people. The number of side effects reported are rather low. As more studies are conducted, new uses may be discovered and protocols further refined.

If you work rotating shifts or your sleep rhythm has shifted, a good light and dark plan can help; light therapy can be a part of that. Light therapy is also a good strategy if you are older, have mobility issues, and are consequently somewhat deprived of natural daylight.

Conclusion – How does light therapy work?

Light therapy is a powerful method for treating mood disorders and sleep problems by resetting the body’s internal clock. Whether you’re struggling with seasonal affective disorder, sleep problems, or other related conditions, this therapy offers a scientifically proven solution that you can easily incorporate into your daily routine. With the right guidance, light therapy can help improve your mood, boost your energy, and promote healthier sleep habits.

Resources

• Aarts, M., Hartmeyer, S., Morsink, K., Kort, H., & de Kort, Y. (2020). Can special light glasses reduce sleepiness and improve sleep of nightshift workers? A placebo-controlled explorative field study. Clocks & Sleep, 2, 225-245.
• Helmhout, P.H., Timmerman, S., van Drongelen, A., & Bakker, E.W.P. (2022). The effectiveness of blue-light-emitting glasses in security guards exposed to night shift work on work-related and general fatigue: a randomised controlled cross-over study. Clocks & Sleep, 4(4), 675-687.
• Kim, K. et al. (2025). Global prevalence of seasonal affective disorder by latitude: a systematic review and meta-analysis. Journal of Affective Disorders, 390. doi:10.1016/j.jad.2025.119807
• Lam, R.W., Levitt, A.J., Levitan, R.D., et al. (2006). The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. American Journal of Psychiatry, 163(5), 805-812.
• Lambert, G.W., Reid, C., Kaye, D.M., Jennings, G.L., & Esler, M.D. (2002). Effect of sunlight and season on serotonin turnover in the brain. The Lancet, 360(9348), 1840-1842.
• Magnusson, A. (2000). An overview of epidemiological studies on seasonal affective disorder. Acta Psychiatrica Scandinavica, 101(3), 176-184.
• Śmiłowska, K., de Vries, N.M., Bloem, B.R., & van Wamelen, D.J. (2026). Blue light therapy delivered through light glasses improves sleep quality and daytime sleepiness in Parkinson’s disease: a randomized trial. Journal of Parkinson’s Disease. https://doi.org/10.1177/1877718X261468544

Read also: glasses that filter blue light and how daylight saving time affects your sleep.

Light therapy: frequently asked questions