Recent research has demonstrated the significant influence of lighting and thermal conditions on cognitive performance and sleep quality. However, a notable gap exists in understanding how these factors impact older adults within their living environments. This study examined the relationship between daily lighting and thermal exposures with cognitive performance and sleep quality in older adults. Eighteen older adults, with a mean age of 75 (SD = 7.7, female = 13), participated in a three-day study. Throughout the protocol, their indoor lighting and thermal conditions were monitored using environmental sensors. Participants were instructed to complete a series of cognitive tasks twice a day. Additionally, they wore a smartwatch-type actigraph and a wearable light tracker to monitor their sleep/wake patterns and daily light exposure. The findings showed that appropriate nighttime lighting correlated with improved evening cognitive performance. Higher nighttime indoor lighting intensity positively correlated with cognitive measures, while nighttime correlated color temperature (CCT) exposure had negative correlations. Daytime melanopic equivalent daylight illuminance (MEDI) exposure significantly predicted total sleep time, with increased circadian-effective light exposure reducing sleep fragmentation. Conversely, higher nighttime lighting intensity was linked to decreased sleep efficiency. Higher bedroom temperatures were associated with improved sleep efficiency and reduced fragmentation. These findings highlight the importance of optimizing lighting conditions and maintaining comfortable temperatures in residential environments to promote cognitive performance and sleep quality among older adults.