Background Light exposure affects mood and sleep regulation. Sleep problems and mood complaints are common in elderly with intellectual disabilities (ID)living in care facilities. Insufficient light exposure is hypothesised to contribute to the high prevalence of these problems. The current study is the first to describe the personal light exposure pattern during the waking day in elderly with ID. Methods The study sample consists of82elderlywith ID (aged62.3±9.4years) living in16residentialhomes of three care organisations in the Netherlands.Personal light exposure was measured continuouslyfor7–10days using a HOBO data logger light sensor,measuring illuminance at chest height. Participants wore a wrist-worn accelerometer (Actiwatch or Geneactiv) to indicate the bedtimes to determine the waking day. Results The variation in illuminance is small during the waking day. Elderly with ID spend most of their waking day (mean duration =14:32:43h) in dim light(1–500lux) environment and spend a median of32min in light>1000lux. Within participants, the threshold associated with better sleep (>50min of light>1000lux) was reached for34% of the days,and the threshold associated with less depressive symptoms (>30min of light>1000lux) was reachedin46% of the days. Exposure>1000lux was lower during weekends than during weekdays. Conclusion Elderly with ID spend most of their waking day in low light levels and did not meet the proposed values associated with better sleep and mood. Given the importance of adequate light exposure for regulation of sleep and mood, and the prevalence of sleep and mood problems in elderly with ID, the current study suggests that the lit environment for this already frail population should be given more attention.