To understand the various exercises into sunlighting one must go back to the origins of daylighting and sunlighting design in the 1920s and 1930s when health was considered of importance enough to require large windows and fully openable verandahs in our schools. The problems were as many as the benefits so that by the late 1940s, legislation was introduced to fix the daylighting quality and so the 5% daylight factor (DF) was introduced as a design aim. Later, in the 1950s, daylight factor was re-defined and a 2% DF minimum target was introduced, the previous 5% being properly identified as a Sky Factor.