On the calculation and measurement of mean room surface exitance

Abstract

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.

A fresh approach to interior lighting design: The design objective – direct flux procedure

“…Serves as the measure of ambient illumination within an enclosed space. MRSE may be predicted by Duff's precise method, 9 or estimated by Cuttle's formula, [1][2][3] MRSE ¼ FRF=A.…”

“…The scope of Duff's studies of exitancebased metrics is extensive. He developed procedures for measurement and calculation; 9 he compared the accuracy of alternative prediction formulae 10 and he conducted experiments which involved subjects making subjective assessments of their surrounding environments. 11,12 The outcomes of these experiments are examined in the following section and are shown to be particularly relevant to this paper.…”

“…As part of Duff's assessment of the accuracy of alternative predictive formulae, 10 he compared MRSE values calculated for a reference room by his own definitive procedure (equation 1) 9 with values calculated by Cuttle's The relative values shown in the chart indicate that if all room surfaces are of the same reflectance, then for providing MRSE, it makes no difference how the flux is distributed. For conventionally decorated spaces, where ceilings are lighter and floors are darker than walls, then as reflectance diversity increases, so the efficiency of indirect lighting to provide MRSE increases, and the efficiency of direct lighting reduces.…”

“…While MRSE is a reasonably straightforward concept, its measurement does create difficulty as it requires an instrument that distinguishes between diffusely reflected light from room surfaces and light directly incident from luminaires or windows. This has been addressed by Duff et al, 9 who have applied commercially available high dynamic range imaging equipment to perform MRSE measurements, and while these researchers have demonstrated the feasibility of a practical MRSE light meter, it again requires acceptance of the concept for suitable instruments to become available.…”

Calculation and measurement of mean room surface exitance: The accuracy evaluation

“…The idea of MRSE attracts much attention and discussion. 5–11 However, the successful adoption of this new concept in lighting applications may largely depend on research advances in the following aspects: (i) experimental evidence of MRSE being clearly linked to people’s assessment of brightness appearance, (ii) an easy way to calculate MRSE, and (iii) a practical method to measure MRSE in the field. For the link between MRSE and brightness appearance, Cuttle 4 has shown that, through subject assessments, MRSE and scene brightness are linearly related.…”