Light therapy

A very small study with n = 29 adults found positive effects of early morning light therapy in the fall/winter months on objective and subjective ADHD symptoms, mood and a shift in the circadian rhythm.¹ The shift in the circadian rhythm appeared to have the greatest influence on the improvement of ADHD symptoms. Another, even smaller study on 16 adults came to similar conclusions.²
A third placebo-controlled study comparing the circadian rhythm with melatonin or melatonin plus light therapy also found that light therapy (here: as an addition to treatment with melatonin) could shift the circadian rhythm forward and that this had positive effects on ADHD symptoms. Melatonin alone had a stronger effect than light therapy, light therapy improved the result of melatonin treatment.³
A review confirmed these results.⁴

Initial studies used illuminance levels of 2,500 lux. Today, an illuminance of 10,000 lux is typically used. (Illuminance: amount of light on an illuminated object at a defined distance from the light source).
When using a daylight therapy lamp, a treatment time of 30 minutes is usually required, during which the patient looks directly into the lamp from a distance of 20 cm (always observe the relevant operating instructions!). Simply switching it on to read is not sufficient.
Alternatively, there are light glasses that can be worn while reading
It is important to ensure that the light has a high blue component. Daylight has 5,000 to 25,000 Kelvin.

It is important to use light therapy for ADHD in the early morning, as the aim is to shift the circadian rhythm forward.
In some disorders, the circadian rhythm is already too far ahead, so that light therapy would be disadvantageous here

A combination with exercise (early morning walk, early morning sport) is likely to be more effective, as exercise is another zeitgeber. Early food intake (breakfast) is also likely to keep the circadian system in an early rhythm.