Light is not visible; light makes other things visible. A room without openings or sources of artificial light is quite simply dark. So it is all about making the environment visible, enabling us to see things. Light is the basis for visual perception. Light creates hierarchies, distinguishes the important from the unimportant, divides the space into zones and/or focuses attention and serves as a natural clock for us human beings. The biological and emotional effect of light is of great importance, particularly in today's supersaturated multi-media world.