Seasonal affective disorder (SAD) is a type of depression triggered by the long nights of winter in the world's higher latitudes. It affects up to a tenth of the population in those regions. The exact physiological underpinnings are not clear; possible culprits include lower levels of melatonin (a hormone regulating sleeping patterns), a drop in serotonin (a neurotransmitter) and disruption to the body's internal circadian clock.
Many sufferers treat the condition with gadgets designed to emit bright light, from devices resembling desk lamps to ones that look like a tablet on a stand. Many doctors recommend light therapy as a first-line treatment.
A 2024 review of 21 studies, led by Tu Zhe-Ming at the Jingzhou Mental Health Centre in China, concluded that light therapy does seem to work. A review published in March 2025 by Mihaela Bucuta at the Lucian Blaga University of Sibiu in Romania concluded that between 60% and 90% of patients see symptom remission with daily use.
Devices emitting predominantly blue, green or white light all seem to have a similar impact. Many lamps advertise brightnesses of around 10,000 lux—far brighter than standard indoor lighting and closer to a reasonably nice day outdoors—but less intense light seems to work too, though the lamp may need to be on for longer. Side-effects such as headaches, eye irritation and blurred vision are rare.
Research suggests light therapy can also help patients with non-SAD forms of depression. Dr Bucuta's review concluded that light therapy by itself can help with depression in 44% of cases; combined with antidepressants, that number rises to 76%. Experiments comparing drug or light therapy alone with a combination of the two suggest that doing both together produces better results than taking drugs alone.
The more they over-think the plumbing the easier it is to stop up the drain.