Architectural lighting design focuses on three fundamental aspects of the illumination of buildings or spaces. The first is the aesthetic appeal of a building, an aspect particularly important in the illumination of retail environments. Secondly, the ergonomic aspect: the measure of how much of a function the lighting plays. Thirdly is energy efficiency, ensuring that light is not wasted by over-illumination which occurs either by illuminating vacant spaces unnecessarily or by providing more light than needed for the aesthetics or the task.