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Severely depressed patients not only see the light but turn from SAD to glad while wearing an unusual hat fitted with two fluorescent tubes, according to researchers who hope to help millions with the device.

The invention is a hat that looks like a pith helmet with the two tubes placed parallel to the eyebrows. It was designed as a portable, wearable way to treat patients suffering from a severe form of winter depression, dubbed seasonal affective disorder or SAD."Almost everyone I know can't stand February and looks forward to spring," said Dr. George Brainard, a neurologist who along with biomedical engineer Dan Benson developed the hat at Thomas Jefferson University.

But, he said, the victims of SAD have an "outright lack of energy and an inability to cope."

SAD is characterized by withdrawal, social isolation, depression, a craving for carbohydrates, weight gain, a tendency to sleep longer and fatigue. People with SAD generally improve as springtime's sunnier days grow closer.

Scientists estimate that SAD severely afflicts about 10 million Americans. About 25 million experience a milder form of the disorder. Most of the cases occur in the northern states, where days are shorter.

Researchers have found that exposure to bright light, or phototherapy, alters the production of the hormone melatonin and relieves the depression.

Brainard said researchers believe the therapy works because light directed into the eyes stimulates a region of the brain called the hypothalamus, which controls production of hormones, including melatonin.

How light works to alter hormone production and relieve depression is not known, he said.

The two, 6-inch lights - five times as bright as the light in a well-lit room - fit under the brim of the hat, which is attached by a cord to a battery pack worn on a shoulder strap.

Brainard and Benson designed the first prototype two years ago. This month, they began testing the hat on six patients with SAD and hope to treat up to 20 this season.

"In 85 percent of SAD cases, light therapy has caused a significant improvement or complete relief of all symptoms," said Brainard.

But most patients can't spend their days outside in bright sunshine. The light hat enables people to fit the phototherapy into their busy lives by wearing the hat at home.

Patients wear the hat for about two hours a day, usually in the morning, said Karen Stewart, director of Jefferson's SAD clinic.