Sleep onset insomnia may be associated with a delayed circadian rhythm. The present study investigated the effectiveness of 1-week of bright morning light exposure in advancing the urinary melatonin rhythm and improving the sleep and daytime functioning of individuals with sleep onset insomnia. The participants were assigned to either a bright-light condition (2500 lux) or a control, dim red light condition (100 lux). Sleep, insomnia severity and daytime functioning were monitored using sleep diaries, activity monitors and questionnaires during the pre-treatment and 3-week post treatment period. While there were no significant changes in the dim light control group, the bright light group had a significant 1 h 21 min phase advance of melatonin onset. Compared to pre-treatment measures, over the 3-week follow-up period, the brightlight group had a greater decrease of sleep onset latency, a significant advance of sleep onset time and a significant increase of total sleep time of 51-min. The participants in the bright light group also reported a decrease in insomnia severity, less presleep (cognitive) anxiety and improved overall daytime functioning as well as less daytime fatigue and sleepiness than the control group. The study demonstrated that 1 week of bright morning light exposure can advance the melatonin onset and improve the sleep and daytime feelings of individuals with sleep onset insomnia whose circadian rhythm is relatively delayed.