chapter  14
Daylight Calculations
Pages 19

Much study and thought has been given to these factors and appropriate assumptions and approximations have been adopted, so that daylighting of buildings can be quantified.

In countries such as the UK, where completely overcast skies are a common feature, the criteria are based upon the relative illuminance inside a room to that under the unobstructed overcast sky at the same moment in time. The ratio of these illuminances is called the daylight factor (dJ) and is expressed as a percentage. The daylight factor includes interreflected light and can be for a point, a surface or the average for the room.