The provision of daylight in a building is strongly linked to the spatial and architectural design. Unlike other environ mental services, the elements of daylighting-windows and surfaces-are surely the most visual and expressive. For this reason windows have a long history of attention from architects; indeed, architectural style has been defined by patterns of fenestration probably more than by any other single characteristic. It should be of interest then, to the architect, that daylighting design also has a strong influence on both the energy use of a building and the general comfort and well-being of the occupants (Figure 6.1).