Limiting ratios of luminance and illuminance

Abstract

The limiting illuminance ratio recommendations in the 1977 IES Code are reviewed. The following alternative criteria are proposed: (a) the current ceiling/task illuminance ratio limits should be replaced by a recommendation that the ratio of ceiling luminance (asb) to task illuminance (lux) should lie between 0.2 and 0.6; (b) the current lower limiting wall/task illuminance ratio (0.5) should be supplemented by a recommendation that the ceiling luminance (asb) should not exceed the wall illuminance (lux); and (c) there should be no upper limiting wall/task illuminance ratio; the limiting glare index would effectively control this ratio. A simple device is described for measuring ratios of ceiling luminance to wall or task illuminance.