Abstract
Hopkinson's multiple criterion scale is widely used to investigate the subjective degree of discomfort due to glare. Using an adjustment procedure, glare source luminance is adjusted to reveal four levels of discomfort, typically: just imperceptible, just acceptable, just uncomfortable, and just intolerable. In many studies, observers are instructed to attend to each level of discomfort in ascending order, from the lowest to the highest criterion. It is likely, however, that any settings made using this approach are influenced by an order bias, and this would affect the reported thresholds of discomfort. To investigate order effects, a Hopkinson-like multiple criterion adjustment experiment was performed, but under three different order sequences: ascending, descending, and randomised. The results revealed substantial bias due to order effects, particularly for lower glare criteria. This demonstrates the need for caution when interpreting subjective evaluations of discomfort due to glare and estimating the robustness of glare indices derived from studies that used Hopkinson's scale and procedure.
Highlights
The investigation of glare in buildings has led to the development of several predictive models that have been widely used in studies seeking to evaluate the thresholds of visual discomfort caused by artificial lighting sources [1,2] and by daylight [3,4,5]
Visual inspection of the plots suggests that mean source luminances were highest when adjustment settings were made using a descending sequence for each glare criterion
The standard deviations about the mean source luminances become larger when adjustments were made to higher levels of discomfort, and this is consistent across all three order sequences
Summary
The investigation of glare in buildings has led to the development of several predictive models that have been widely used in studies seeking to evaluate the thresholds of visual discomfort caused by artificial lighting sources [1,2] and by daylight [3,4,5]. There have been advancements in the way in which discomfort caused by glare is measured – for example, using photographic techniques and image analysis software in the evaluation of daylit environments [7,8] – much less attention has been placed on experimental procedures. In this context, Hopkinson's 1940 paper [9] is commonly recognised as the founding study of discomfort due to glare. These corresponded to four criteria describing different degrees of discomfort due to glare: the multiple criterion scale (MCS) (Table 1)
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