A practical method for field measurement of mean room surface exitance

Cuttle has proposed to use mean room surface exitance (MRSE) as a measure of spatial brightness for interior lighting design. One problem hindering the adoption of MRSE is the lack of a practical field-measurement method with verified accuracy. Although Cuttle suggested that MRSE can be estimated by measuring the illuminance caused by indirect light from a position that takes up an overall view of the room, no evidence was provided and that approach was later proved to be inaccurate. This paper presents a newly developed approach for measuring MRSE in a conventional cuboid space, simply by placing an illuminance meter at specific locations, recording the illuminance values caused by indirect light and calculating the weighted average of those values. The weighting parameters can be determined based on the geometry of the space. Furthermore, the rationality of such an MRSE-measurement method is provided, and its accuracy is verified by using Radiance lighting simulation, which suggests an error of less than 10%. Our proposed method shows that measuring MRSE in the field is feasible.