Objective: To compare the efficacy of 20 min versus 45 min light exposure for relieving psychophysiological insomnia in the elderly. Methods: Prospective recruitment of subjects 60 years and older with psychophysiological insomnia. Random distribution to 20 or 45 min of daily exposure to 10,000 lux for 60 days. Sleep latency, total sleep time, fatigue and activity were measured at baseline and 3 and 6 months posttreatment. Blind analysis of data and comparison were performed using repeated-measure analysis of variance, independent samples t test and Wilcoxon rank signed test. Results: At 3 months, improvement was significantly higher in the 45-min versus 20-min condition. At 6 months, variables returned toward baseline in the 20-min but not in the 45-min condition. Conclusions: Twenty minutes of bright light treatment leads to a lesser treatment response than 45 min at 3-month follow-up and to a return toward baseline at 6-month follow-up that was not seen with a 45-min exposure. (C) 2004 Elsevier Inc. All rights reserved.