The purpose of this paper is to encourage discussion on whether the acceptable standards of natural illumination have increased since Colls was decided in 1904. It invites discussion as to whether new parameters should be set or whether the 50/50 rule should be changed. Reference is made to the circumstances in which the grumble point of 0.2 per cent was calculated and to the method of measuring this accurately with the aid of a Waldram diagram. Comments are invited from readers to continue the debate.
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