Discomfort glare evaluation: The influence of anchor bias in luminance adjustments

Mg Kent,S Altomonte,S Fotios

doi:10.1177/1477153517734280

Mg Kent, S Altomonte + Show 1 more

Open Access

https://doi.org/10.1177/1477153517734280

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Abstract

Luminance adjustment is a procedure commonly used to evaluate discomfort glare and the results from adjustment experiments form the basis of some recommendations for limiting its occurrence. There are, however, strong reasons to expect that settings made using adjustment are unintentionally influenced by extraneous variables. This paper discusses bias towards the initial anchor, the setting of the variable stimulus immediately before an adjustment is made. Specifically, the initial luminance is expected to influence the setting that is made by adjustment; for example, a lower initial luminance leads to a lower setting than a high initial luminance. To investigate anchor bias, a Hopkinson-like multiple-criterion adjustment experiment was undertaken, but with three different anchors. The results confirmed significant bias: glare settings were biased towards the luminance of the initial anchor. This demonstrates a need for caution when using adjustment to explore discomfort glare and when interpreting the results of past studies that used discomfort glare models fitted to data obtained with this procedure.

Highlights

IntroductionUnified Glare Rating (UGR) describes the level of discomfort due to glare according to the luminance, size, and location of the light source, and the luminance of the background !
The results show that, for the same level of glare sensation reported across the three initial anchors, the mean values of Illuminating Engineering Society Glare Index (IES-GI) correspond to different discomfort glare criteria
The results from this study provide statistically significant and substantive evidence that, in a controlled laboratory experiment, adjustment tasks used to test the degrees of glare sensation from a bright light source are biased by the initial luminance setting

Summary

Introduction

UGR describes the level of discomfort due to glare according to the luminance, size, and location of the light source, and the luminance of the background !. L2s Á os P2s ð1Þ where Ls 1⁄4 source luminance (cd/m2), xs 1⁄4 subtended solid angle of the glare source (sr), Lb 1⁄4 background luminance (cd/m2), P 1⁄4 Guth’s position index (–). The UGR is a development of the Illuminating Engineering Society Glare Index (IES-GI),[6] but with an alternative approach to account for the luminance of the background.[7,8] The IES-GI (equation (2)). Is itself a development of the Glare Constant (equation (3)) established in the discomfort glare studies of Petherbridge and Hopkinson,[9] but with a logarithmic function to account for the sensitivity of the visual system[10] Models of discomfort glare Discomfort glare is generally defined as a psychological sensation that causes distraction or annoyance without necessarily being linked to a reduction in visual ability.[1,2] This discomfort arises from the luminance of a light source (or luminance contrast) within the visual field of an observer that is sufficiently greater than the conditions to which the eyes are able to adapt to.[3]

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