This paper presents a pilot study that investigated the suitability of mean room surface exitance as a predictor of spatial brightness and perceived adequacy of illumination, then compared these results with how horizontal illuminance predicted both items under the same conditions. An experiment used 26 participants and a small office. It exposed participants to three levels of mean room surface exitance, each delivered with three different light distributions and across three different surface reflectances, resulting in a total of 27 light scenes. A clear relationship existed between mean room surface exitance and both perceived adequacy of illumination and spatial brightness, but not between horizontal illuminance and either item. Correlations were drawn between reported levels of spatial brightness and reported levels of perceived adequacy of illumination.

Cuttle has proposed mean room surface exitance as a metric for use within interior lighting design. Two reported barriers to its use are; a lack of available software to calculate the metric and the tedious and cumbersome nature of recording its values in the field using current equipment and methodologies. This paper presents a method for facilitating the calculation of mean room surface exitance using readily available freeware, namely Radiance, and also presents a methodology that utilises high dynamic range imaging as a pragmatic alternative for field measurement.

This paper presents a pilot study that has investigated the suitability of mean room surface exitance as a predictor of spatial brightness and compared these results with how horizontal illuminance predicts spatial brightness under the same conditions. The experiment took a group of 26 participants and, using a scaled booth, exposed each participant to three levels of mean room surface exitance, each delivered with three different light distributions and three different surface reflectances, resulting in a total of 27 light scenes. Results demonstrated that, under the range of conditions to which participants were exposed, a systematic relationship existed between mean room surface exitance and spatial brightness, but not between horizontal illuminance and spatial brightness.

Two formulae currently exist for calculating mean room surface exitance. This research note explains and demonstrates that one of these formulae is erroneous under certain conditions and stresses that the alternative expression should generally be used for computing mean room surface exitance.

A recent editorial in Lighting Research and Technology 1 suggested the need for 'a simple set of questions to ask the LED supplier'. This letter presents such a set of questions, but also, and perhaps more importantly, a set of responses that might be considered appropriate. The information used to form these questions and answers has been drawn from a number of useful resources, 2-7 interaction with various lighting professionals and through the author's own experience. The purpose of these questions is to generate discussion. The author understands the questions posed can be improved upon and it is hoped that this will happen in a constructive and iterative manner.