This dissertation investigates the effect of the geometry of external shading devices upon light distribution, air flow pattern and thermal comfort, with direct application to the tropical hot-humid climates. A series of 30 different configurations of shading devices were evaluated under four different testing conditions, including overcast and clear sky for daylighting, and perpendicular and oblique winds for natural ventilation. The total of 120 tests on identical size scale models, was undertaken at the V.P.I. & S.U. Environmental Systems Lab via a low-speed wind tunnel (for air flow pattern) and an artificial skydome and real sky (for light distribution), with the use of conventional measurement devices. This research has made progress toward the goal of providing a framework to collect performance data and to display it in a graphical format, so that direct comparison can be made. This simultaneous reporting proved to be important since it facilitates a determination of whether natural lighting is being obtained at the expense of ventilation or whether the lighting has been sacrificed for ventilation, as related to human comfort. It demonstrates that no shading devices, either horizontal, vertical or combination, behave identically under identical conditions. Through the analytical model, this research has described a procedure by which designers can identify and select, from the performance data, the most effective use of shading devices based on their optimal characteristics. It provides the information about achieveable levels of performance of the given shading configuration and a prescriptive way on how that performance can be achieved. It also serves as a basis for a more systematic approach, and demonstrates that the amount of experimental work required to investigate the wide range of shading possibilities, while certainly formidable, is not excessive. / Ph. D.