Discomfort from glare

Despite nearly a century of research, we are still unable to accurately predict discomfort due to glare.

The vast majority of discomfort glare research uses subjective evaluations – primarily category rating or luminance adjustment. This article discusses methodological issues which contribute to uncertainty in evaluations.

Fotios S. Research Note: Uncertainty in subjective evaluation of discomfort glare. Lighting Research and Technology, 2015; 47(3); 379-383.

It is unlikely that the commonly used procedures will ever reach resolution. This article raised suggestions for alternative procedures.

Fotios S. Correspondence: New methods for the evaluation of discomfort glare. Lighting Research and Technology 2018; 50(3): 489-491.

Evaluations of discomfort using category rating were compared against involuntary physiological responses.

Subjective evaluation of discomfort was highly correlated with eye movement and pupil constriction: Severe glare discomfort increased the speed of eye movement and caused larger pupil constriction.

Lin Y, Fotios S, Wei M, Liu Y, Guo W, Sun Y. Eye movement and pupil size constriction under discomfort glare. Investigative Ophthalmology and Visual Science, 2015; 56(3); 1649-1656.

A series of experiments were conducted by Michael Kent to explore the influence of variations in experimental design, the aim being to explain the variance between different studies.

In this first experiment we explored the influence of anchor bias in luminance adjustments.

Kent M, Fotios S, Altomonte S. Discomfort glare evaluation: The influence of anchor bias in luminance adjustments. Lighting Research and Technology 2019; 51(1): 131-146.

When Hopkinson used his multiple criterion scale, test participants used adjustment to set the luminance representing a defined degree of discomfort. One limitation was that the four degrees of discomfort were evaluated only in ascending order.

In this experiment we repeated Hopkinson’s method but also using descending and randomised orders of discomfort. The different orders led to significant differences in luminance for a given degree of discomfort.

Kent MG, Fotios S, Altomonte S. Order effects when using Hopkinson’s multiple criterion scale of discomfort due to glare. Building & Environment 2018; 136: 54-61.

When evaluating discomfort the test participant must look somewhere, and for evaluating discomfort from peripheral sources a fixation task is used. This experiment compared the use of a simple fixation mark and a task requiring a degree of cognitive attention. The results confirmed a lower degree of discomfort is expressed when engaged in a task demanding a higher degree of cognitive attention.

Kent M, Fotios S, Altomonte S. An experimental study on the effect of visual tasks on discomfort due to peripheral glare. Leukos. 2019; 51(1): 17-28.

Stimulus range bias is probably the greatest problem within subjective evaluations of magnitude. Here we demonstrate its influence on evaluations of discomfort from glare using adjustment. The conclusion, that range bias is significant, is not unexpected but direct demonstration helps to support the message.

Kent MG, Fotios S, Cheung T. Stimulus range bias leads to different settings when using luminance adjustment to evaluate discomfort due to glare. Building & Environment 2019; 153; 281-287.

When you ask test participants to evaluate a series of items which vary in magnitude, it has been proposed that first the range is demonstrated. In other words, before any evaluations, show participants the smallest and largest magnitudes they are about to evaluate. This helps anchor the response range to the magnitudes. This experiment was conducted to determine whether such demonstration would affect the evaluations.

Kent M, Fotios S. The effect of a pre-trial range demonstration on subjective evaluations using category rating of discomfort due to glare. Leukos 2021; 17(1): 43-58.

Jan Wienold (EPFL) and several colleagues recently published a paper in which they tested several possible metrics for discomfort from daylight glare using a several independent sets of data. In terms of a robust analysis, this was outstanding work. In this item of correspondence I raised a few of questions. One question asked about fairness, given that the proposers of the two best-performing models are also authors of the analysis. A further question asked about stimulus range bias: the authors had suggested it was not a problem but that is unlikely to be the case.

Fotios S. Correspondence: Discussion of ‘The cross validation and robustness of daylight glare metrics’ Lighting Research and Technology 2020; 52(2): 314-317.

Glare can impair vision (disability) as well as causing discomfort.

This article describes an experiment conducted to investigate how disability glare can affect target detection.

Winter J, Fotios S, Völker S. The effects of glare and inhomogeneous visual fields on contrast detection in the context of driving. Lighting Research and Technology 2018; 50(4): 537-551.

This is a review of th emethods used to measure the discomfort imposed by glare. It shows there are many sources of bias in measurement. A key issue is stimulus range bias, which confounds the translation of what should be considered a relative judgement (one scene is more glaring than another) into an absolute judgement (this scene represents a certain magnitude of discomfort). Until better acknowledgement is given to stimulus range bias it is unlikely that metrics for discomfort from glare will have any validity.

Fotios S, Kent M. Measuring discomfort from glare: Recommendations for good practise. Leukos. 2021; 17(4): 338-358

Many previous studies of discomfort from glare have used category rating to measure the degree of discomfort. One problem in these studies, in particular those studies of outdoor lighting using the de Boer scale, is that the magnitude labels on the scale are not always easy to understand. In some scales there is no option to say that discomfort is not apparant.

In this paper we propose an alternative scale. This is a two stage approach. First, a yes/no response as to whether or not there is any discomfort. If there is, and only if there is, the participant then rates the magnitude using a scale with labels that should be less confusing.

Hickcox KS, Fotios S, Abboushi B, Miller N. Correspondence: A new two-step approach for evaluating discomfort from glare. Lighting Research and Technology 2022; 54(1): 91-92.

Ongoing work

With colleagues from the IES Discomfort Glare in Outdoor Nighttime Environments (DGONE) we are working towards a metric for charactering discomfort.