Abstract
A general method of determining utilization factors for luminous ceiling installations is given in IES Technical Report No. 2; this includes the uniformly diffusing ceiling. With the wider use of luminous ceilings, new materials and systems of light control have been introduced and early experience using some of the newer materials indicated the need for special care in the application of the Technical Report No. 2 procedure if errors were to be avoided. This paper reports the results of an investigation in which calculated values of workplane illuminance were compared with measured values in practical installations incorporating the newer materials. It is shown that if exact values of utilization factors are to be obtained precise calculation and photometric data are necessary. The method of design given in Technical Report No. 2 is valid for these installations, but a different procedure for calculating the cavity light output ratio is needed to improve the accuracy of the calculated utilization factors.
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