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 the energy efficiency issue to assure that light is not wasted by over-illumination, either by illuminating vacant spaces unnecessarily or by providing more light than needed for the aesthetics or the task.
Each of these three aspects is looked at in considerable detail when the lighting designer is at work. In aesthetic appeal, the lighting designer attempts to raise the general attractiveness of the design, measure whether it should be subtly blended into the background or whether it should stand out, and assess what kind of emotions the lighting should evoke. The functional aspects of the project can encompass the need for the project to be visible (by night mostly, but also by day), the impact of daylight on the project and safety issues (glare, colour confusion etc.).
Architectural lighting design, much like architecture itself, qualifies as being neither an art nor a science, rather a mixture of both. While creative spirit is demanded of a designer, a qualified professional architectural lighting designer will generally have a good understanding of the properties of light from a scientific standpoint and of the functioning of a light fixture (known as a "luminaire" in field terminology).