Green Buildings and Potential Electric Light Energy Savings

This paper estimates the approximate yearly electric lighting load of a “green” commercial building for a temperate climate region by studying the impact of a large curved south-facing facade with an external horizontal shading louver, a high window location, and a specular light shelf on yearly interior daylight levels, based on hourly weather data for Washington, D.C. Thus the paper determines the required electric light quantity by calculating hourly daylight illuminance levels and deriving required electric fill-in light when daylight levels are too low, determining daylight quality by calculating luminance values and luminance ratios used for office lighting criteria. It is found that electric light in lux hours per year is needed only for 16% of yearly office hours. The paper gives recommendations for window size and shape, location, light shelf geometry, ceiling and wall details, and workstation layout in order to achieve these low lighting loads.