A simulator that mimics the atmosphere of dawn may reduce depression linked to lack of winter sun, say scientists.
Sunlight is probably good for our psyche
They claim the machine, which boosts light levels during sleep, is an effective treatment for Seasonal Affective Disorder (SAD).
The study, published in the American Journal of Psychiatry, also backed devices which emit negatively-charged oxygen particles.
The condition affects thousands of people in the UK.
Experts here recommend light treatment, changes in diet and increased exercise to beat it.
Exposure to sunlight helps the body produce serotonin, a body chemical which promotes feelings of well-being.
Many sufferers spend 30 minutes or more each day sitting by a bright "light box" to combat SAD, but the "dawn simulator" works while the person is asleep.
It reproduces the gradually rising light levels of a May day, while the negatively-charged ions attempt to copy atmospheric conditions outside the home.
Dr Michael Terman, who led the study, gave 99 volunteers with SAD one of five different treatments - conventional light therapy after waking, two types of dawn simulation and two types of negative ionisation therapy.
A full dawn simulation and one type of ionisation were equally successful.
Improvement was seen in 57% of subjects in the bright light therapy, 50% of those in the dawn simulation group and 48% in the high air ionization group.
Dr Terman said while many people would continue with bright light therapy, the dawn simulation and ionisation might be worth considering as an alternative.
"Dawn simulation and negative air ionisation are two naturalistic, non-pharmaceutical environmental enhancements now verified superior to placebo and remarkably effective in the treatment of winter depression."
Alison Cobb, a policy officer at the mental health charity Mind, said there were other alternatives which might alleviate seasonal depression.
She said: "In addition to light therapy, there are lots of other proven ways to lift your mood which you can try.
"Eating the right diet, with slow energy release food, and cutting down on caffeine can help regulate your mood and sleep.
"We'd recommend some gentle exercise such as a walk, as there's plenty of evidence to suggest that being physically active helps fight depression.
"Try to spend as much time as possible outdoors - even when it's overcast, light levels will be higher than indoors."