Abstract
A luminaire domain chart maps artificial lighting systems in terms of their direct ratios and flux fraction ratios. It is shown that loci of constant planar utilance and loci of constant illuminance ratios can be plotted as straight lines on such a chart. The concept of 'unreal' luminaires, mathematically defined, extends the chart beyond the domain of real luminaires, and enables it to be used as a simple nomogram for design purposes. A limiting quadrilateral is bounded by four straight lines corresponding to the upper and lower permissible illuminance ratios. Lighting systems falling within this quadrilateral satisfy all illuminance ratio requirements. Loci of constant utilance are identified. The effects of surface reflectances on illuminance ratios are discussed.
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