The recent amalgamation of the Illuminating Engineering Society of Great Britain (IES) with the Institution of Heating and Ventilating Engineers to form the Chartered Institution of Building Services Engineers (CIBSE) provided an opportunity to replace the old IES publication "Daytime Lighting in Buildings" with a new window design manual. This targeted both architects and engineers and embraced all aspects of window performance including view, heat loss, and heat gain, as well as quality and quantity of natural lighting and its implications for electric lighting designers. Window areas can be optimised by balancing the conflicting lighting and thermal considerations. The shape and position of a window can be optimised by balancing aspects of visual comfort, view, uniformity, and glare. The window design manual places these decisions in a logical sequence.

KEYWORDS: windows, designing, heat loss, heat gain, handbooks, natural lighting.