Variation and use of contrast rendering factor and equivalent sphere illuminance

Abstract

Measurements have been made of Contrast Rendering Factor (CRF) at various task positions in a small office for a variety of lighting installations and visual tasks. Computer programs have also been used to calculate CRF and Equivalent Sphere Illuminance (ESI).

The principal determinant of CRF was the presence or absence of a luminaire in the offending zone. Visual tasks of different specularity showed similar patterns of CRF variation but to different degrees. Luminaire size and position showed some effect on CRF, but the light output distribution of the luminaires had only a small influence. The computer calculations showed similar trends to the measured values. The use of CRF as a criterion of lighting quality is advocated.

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