This study aimed to examine the effect of bright white light on the fatigue level and sleep quality of cancer patients receiving palliative care. The study sample consisted of 52 patients who met the inclusion criteria and were assigned to the study or control group by stratified randomization. The bright white light (10,000 lux) or dim red light (<50 lux) was applied for 30 minutes every morning for 14 days to the patients in the study and control group. In the study, bright white light significantly decreased the level of fatigue and the level of fatigue-related effect on daily life activities, improved sleep quality and increased total sleep time ( p < 0.05). It was found that dim red light significantly decreased the level of fatigue and increased the sleep quality, but this change was lower than the study group ( p < 0.05).