Cancer related fatigue (CRF) - a persistent sense of exhaustion related to cancer or cancer treatment - can severely interfere with activities of daily living, and has even been reported to be a factor in patient requests for hastened death. CRF can represent a serious clinical problem years after all treatment has ended. There is currently no effective treatment for CRF. The purpose of this study is to investigate whether systematic exposure to light (from a commercially available Litebook) reduces CRF or other symptoms.