A GUIDING LIGHT?


Academics Kit Cuttle and John Mardaljevic debate the relevance of the daylight factor: would people be better off ignoring the advice of the lighting profession, or should the standards be improved?


THE INTUITIVE ARGUMENT KIT CUTTLE


As discussion among lighting professionals revolves around the role of the horizontal working plane, it is generally overlooked that this concept remains fi rmly embedded in the defi nition of the daylight factor (DF) – and, furthermore, that this factor is becoming ever more prominent in sustainability regulations and guidelines. Really, we all understand daylight. In our


living rooms we arrange the furniture for view and for that sense of contact with the outside, and to allow a fl ow of light into the space that creates light and shade patterns, within which we can place an object, such as a vase of fl owers, to ‘catch the light’. We do this intuitively and derive pleasure from the ever- changing visual effects. But then if we fi nd ourselves involved on


So, with all this computational power at out elbows, why are architects not beating paths to our doors for advice? Why are they doggedly hanging on to control of everything to do with windows? – Kit Cuttle


a project where someone mentions daylight, we forget all that intuitive stuff and switch into technocrat mode. The distribution of daylight is specifi ed in terms of the daylight factor, being the daylight illuminance at a point on the horizontal work plane, relative to the simultaneous illuminance due to an unobstructed ‘standard overcast sky’. This concept is supposed to enable us to evaluate daylight objectively – that is to say, to treat daylight as an alternative source for providing work plane illuminance. And it has become so much easier to do


this. The protractors, graphical techniques and tables of data developed in the last century to enable point-by-point calculations were tedious to use, but these have given way to computer programs that generate colour-coded DF


14 CIBSE Journal December 2012 www.cibsejournal.com


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