This research investigates the theoretical and experimental performance of the newly combined TDD/SWH (Tubular Daylight Device and Solar Water Heating) system. A novel proposed system was implemented to convert solar energy into two useful energies; light and heat simultaneously under climatic circumstances of Egypt with the same occupied space. A detailed thermodynamic model was developed to predict the performances of the TDD/SWH system. The system performance was analyzed theoretically and experimentally against time, variable temperature and incident sunlight. The experimentally recorded measurements that include the total and diffuse radiations, absorber, inlet collector, exit collector and inside water tank temperature are compared with those obtained by theoretical analysis. Additionally, three daily performances were done to study the effect of sun insolation and ambient condition on the TDD/SWH system. All measured data was recorded automatically at an interval 30 min. The TDD performance was obtained theoretically and experimentally through the internal and external illuminance. The increasing of inlet water temperature in SWH collector leads to decrease in rate of heat transfer between the collector pipe’s and water. Average hourly and daily performance of SWH was calculated. Finally, the obtained results demonstrate that the proposed theoretical model matched with the experimental work.