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Michael Pitts: Michael Pitts is a Consultant and Former Senior Partner with Edmund Kirby & Sons, a private practice of architects and surveyors where he specialises in rights to light matters. He knew John Anstey for many years. Both followed their respective fathers into rights to light practice and both shared an enjoyment of music making.
Nearly 100 years on from Colls[1], has the time come to re-appraise the point at which man will grumble about the amount of natural light available?
It must be recalled that the factor of 0.2 per cent of an unobstructed hemisphere of uniform sky, as the amount of natural illumination for ordinary purposes below which average reasonable persons would consistently grumble, was arrived at as a result of measurement in public and private buildings carried out in 1912. (This percentage factor was the result of the findings, on the one hand, that the average level of illumination from the whole sky on a dull day in winter was 500 lumens and, on the other, that one lumen per square foot, or one foot-candle, was the level of natural illumination below which the average person would complain.) At this time artificial illumination was generally of a much lower intensity than is available now and until 1923, when P.J. and J.M. Waldram published their paper[2] and their now famous diagram, there were several methods of measuring daylight factor, to differing degrees of accuracy.
The Waldram diagram enables the accurate measurement of the area of sky directly visible from any point within a room at any level. Calculation of the sky visibility contours at any given percentage of an unobstructed hemisphere has been facilitated by the use of computer programs (although the accuracy of those programs in use depends on the number of obstructions with which the program can cope, on the methods used to delineate, e.g. window heads and mullions, and on the accuracy of the information fed in by the operators). The method and equipment are in place to enable courts to consider a new standard[3], but is there the will to change the standard or perhaps establish different standards for, e.g. residential as opposed to office/commercial properties?
As case law developed, it became established that it was not how...