Every fall, like clockwork, Linda Krentz of Beaverton, Oregon, felt her brain go on strike. "I just couldn't get going in the morning," she says. "I'd get depressed and gain 10 poundsevery winter and lose it again in spring. " Then she read about 1seasonal effective disorder, a form of depression that occurs in 2the fall and winter, and she saw the light—literally. Every morning 3now she turns in a specially constructed light box for half an hour 4and sits in front of it to trick her brain into thinking she's still enjoying those long summer days. It seems to work. Krentz is not alone. Scientists estimate that 10 millionAmericans suffer seasonal depression and 25 million more develop 5milder versions. But there's never been definitive proof which 6treatment with very bright lights makes a difference. In all, it's hard 7to do a double-blind test when the subjects can see for themselves whether or not the light is on. That's why nobody has ever separated the real effects of light therapy with placebo(安慰剂)effects. 8 Until now, in three separate studies published last month, researchers report not only that light therapy works better than aplacebo and that treatment is usually more effective in the early 9morning than in the evening. In two of the groups, the placeboproblem was resolved by telling patients what they were comparing 10light boxes to a new anti-depressant device that emits negatively charged ions. The third used the timing of light therapy as the control.