This research discusses the expressive potentialities of natural lighting in architectural design of worship buildings, and how it is employed to convey meanings and feelings that help achieving religious purposes. The study focused on historic worship buildings of Egypt, during two of the most important eras in the history of Egyptian architecture, namely ancient Egyptian and Islamic architecture. The aim of research is to explore how past architects used natural lighting methods to evoke connotations and feelings that reflect concepts of religion and create the appropriate atmosphere for prayer and worship, in order to extract design lessons that can be useful for contemporary practice in architecture. The research adopts comparative analysis approach to compare natural lighting methods in worship buildings during the two eras and interpret their meanings according to the dominant religious concepts during each era. The analysis method includes the study of natural lighting sources inside spaces and their effects in selected examples representing the prevalent types of worship buildings in each era, to inspect how they were utilized to create the suitable atmosphere and imply the appropriate connotations that are required for religious practices.