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In a randomized crossover design, 7 patients with winter depression were treated with 7 d of bright morning light (0600 to 0800) and 7 d of evening light (2000 to 2200). Bright lights in the morning significantly reduced the Hamilton Rating Scale for Depression (HRSD) score (18.4 to 5.0); the bright light in the evening moderately decreased the HRSD score (19.4 to 15.1). The improvement in the HRSD score was significantly greater with morning light than with evening light.
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Avery et al. (1990) studied this question.
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