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. Cultural factors also need to be considered.