Cancer survivors often suffer from chronic fatigue, and when they do, a new study suggests that waking up to bright white light may help them sleep better, reports Reuters.

For the month-long study, researchers had 44 cancer survivors sit very close to a light box early every morning for 30 minutes. The patients were randomly assigned to therapy with either bright white light or dim red light.

More than half of the participants suffered from what’s known as poor sleep efficiency, a measure of how much time in bed people spend asleep. After a month of treatment, however, 86 percent of the people exposed to bright white light had normal sleep efficiency, while 79 percent of the people exposed to dim bright light still had poor sleep efficiency.