The subjective response to linear fluorescent direct/indirect lighting systems

This paper characterizes human subjective response to spatial distributions of light resulting from different uplight/downlight photometric distributions. An array of pendant-mounted linear fluorescent luminaires illuminated a 12.7×7.2 m room. Eleven light settings were established at constant horizontal illuminance, which differed in the percentage horizontal illuminance contribution from the uplight and downlight components. Two studies are reported where subjects evaluated the light settings using psychophysical assessments; the first study utilized paired comparisons and the second utilized semantic differential scaling. Findings include: 1) the walls and the ceiling contributed to the perception of overall brightness when the work plane illuminance was held constant, 2) the room appeared more spacious when more light was supplied indirectly, and 3) light settings where the indirect component had a horizontal illuminance contribution of 60% or more were favoured.