Light Therapy Explained Simply

1. What It Is About

In light therapy, a person sits or stands in front of a lamp emitting light of a specific colour and intensity. The light acts via the eyes or the skin. Some devices resemble bright daylight lamps, others are luminous panels or small, low-intensity spotlights. The treatment is usually administered in a clinic or at home, following a fixed schedule: duration, time of day, and frequency. Originally developed for people with winter depression, three types of light are now distinguished. Blue light affects the body’s internal clock and is primarily studied for sleep problems. Red light and invisible near-infrared light act locally where they are applied, for example at the eye. Invisible ultraviolet light acts on the skin and is used for skin conditions. The effectiveness of a treatment depends on the colour, intensity, time of day, and duration of exposure.

2. What Research Shows

The best-studied application is myopia (short-sightedness) in children; few other areas have as many controlled trials. In one study involving 62 children aged 7 to 15, one group received red light at low intensity. After twelve months, the eyes of these children had grown significantly more slowly than those in the group treated with eye drops containing a myopia-control agent 3. In another study, the eyes resumed faster elongation after treatment ended; this rebound effect has been described 2. In delayed sleep phase syndrome, adolescents struggle to fall asleep at night and have difficulty getting up in the morning. In a study of 49 adolescents, bright light combined with a counselling programme helped them fall asleep more quickly, sleep longer overall, and get up more easily in the morning; these improvements persisted for six months 1. However, the study did not measure whether the adolescents actually used the light regularly. For non-seasonal depression, a review of eleven studies with 858 participants found that adding light therapy to usual care led to moderate improvements in mood, particularly when applied for two to five weeks 5. In vitiligo, a skin condition characterised by depigmented patches, a review examined whether light therapy alone or combined with topical treatments was more effective. While overall results across all skin areas were inconclusive, the combination was superior for the face and neck 4. In these studies, adverse effects were generally mild, such as glare, dry eyes, or itching.

3. What Remains Unclear

The long-term effects of light therapy on the retina remain uncertain. Studies on myopia typically last twelve months, and multi-year follow-ups are still lacking. It is also unclear whether results can be generalised to adolescents, adults, or individuals with high myopia. Another challenge is blinding: since light cannot be concealed, participants usually know whether they are receiving treatment. Many studies therefore lack a true control group. Variations in colour, intensity, and duration across studies make comparisons difficult. Whether there is a clear dose-response relationship is an open question. For ultraviolet light, research highlights a potential risk to the skin, but long-term data are limited.

4. What This Means in Practice

Light therapy is a non-invasive procedure studied across multiple conditions. However, the diversity of applications in existing research makes it difficult to predict individual outcomes. A notable finding is that effectiveness depends on colour, intensity, time of day, and duration, with small changes potentially altering results. Those interested in the topic can find detailed device specifications and protocols in the cited studies. Future research should clarify long-term effects, identify particularly responsive groups, and standardise device specifications to enable better comparability across studies.

All details with study numbers and sources: detailed page on light therapy. For children: Light therapy for children.