Street Lighting Glare: A Study using the measurement of light scatter and fMRI

Lead Research Organisation: University College London
Department Name: Bartlett Sch of Graduate Studies

Abstract

Glare has long been recognised as a problem in street lighting. Glare from street lamps and vehicle headlamps can cause discomfort and a reduction in the conspicuity of objects for both motorists and pedestrians. There is some evidence that the current theory may not explain fully the changes in visual performance that relate to the size and the colour of the glare source. Theoretically the effects of scattering of light and aberrations in the eye have a major impact on retinal image quality. Scattering can cause a loss of visual performance due to discomfort, distraction and reduction in contrast sensitivity. In lighting design terms these effects are known as glare. The problem is usually subdivided into discomfort and disability glare.Recently it has become possible to assess scatter in the eye. The new technique involves direct estimates of light scatter in the eye using imaging techniques. It is both rapid and promises to be significantly more accurate than conventional techniques. This technique is critical to the further investigation of disability glare as it gives the researcher the ability to collect together a group of subjects for whom the veiling luminance in any give scene can be calculated precisely.fMRI is another new tool that has recently been developed to the point where it could be useful in the study of glare. Since its introduction, functional magnetic resonance imaging (fMRI) has become a routine method for mapping neural activity in the human brain. Of key importance to this proposal is that previous fMRI studies have shown an increase in the activation levels within the visual cortex (area V1) with increasing stimulus luminance contrast . Areas V1 and V2/V3 have also been shown to respond reliably and strongly to changes in the luminance of uniform surfaces. These cortical areas are regarded as possible candidates for representing the dimension of perceived brightness.The project will address the following points in order to improve our understanding of the issues associated with glare:Light scatter within the eye is a good predictor of the change in visual performance when glare is present. This will be tested by assessing the light scattering properties of the eyes of a number of subjects in the laboratory and then taking the subjects to the open air test centre and giving them a series of tasks representative of those carried out by pedestrians and drivers at night under different levels of glare.Discomfort glare is a function of source size. This will be tested with a series of laboratory experiments to set the comfort/discomfort threshold for various light source colours, sizes and geometries, and by subjective assessment of different lighting schemes in the outdoor environment.Discomfort glare can reduce visual performance. It has been suggested that there is a relationship between discomfort glare and distraction; if this is the case then discomfort glare may disrupt the processing of complex visual tasks. To test this we will run a series of experiments in the laboratory where the subject has to perform a series of visual tasks that are each relatively easy to see but it is hard to do them all simultaneously. By using a series of different glare sources we will assess the impact of discomfort glare. This will be checked by doing facial recognition tasks in the PAMELA laboratory with different levels of discomfort glare carefully set up so that they provide similar levels of disability glare.Discomfort glare is a real phenomenon and can be detected in the brain. To test this idea we will select from our cohort of subjects a group with differing tolerance to glare. We will study the brain activity the group whilst they are given various visual tasks to do with different levels of discomfort glare. From the fMRI scans we hope to find certain patterns of brain activity that are associated with the sensation of glare.

Publications

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Barbur JL (2012) Changes in color vision with decreasing light level: separating the effects of normal aging from disease. in Journal of the Optical Society of America. A, Optics, image science, and vision

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Davoudian N (2013) Disability glare: A study in simulated road lighting conditions in Lighting Research & Technology

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Konstantakopoulou E (2012) Processing of color signals in female carriers of color vision deficiency. in Journal of vision

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Patterson EJ (2015) Understanding disability glare: light scatter and retinal illuminance as predictors of sensitivity to contrast. in Journal of the Optical Society of America. A, Optics, image science, and vision

 
Description There is massive inter subject variability in susceptibility to discomfort glare. Subjects are also highly variable in the degree to which there eyes scatter light and hence the amount of disability glare they are likely to suffer.

Discomfort Glare in road lighting conditions is a function of retinal illuminance.

Retinal illuminance is largely a function of source luminance, but for very small sources light scatter and problems of focus reduce the actual retinal luminance

Disability glare in the high mesopic conditions (typical of our streets at night) is not as bad as would be theoretically predicted. It is hypothesised that scattered light in the eye increase retinal illuminance and this in turn improves the contrast sensitivity of the retina.

If you compare the cortical activity of people who have lower thresholds of discomfort glare with those who have higher threshold then there are significant differences. In particular there regions of the brain, in the area normally associated with visual processing that are far more active under all conditions in the people who are more susceptible to discomfort glare.
Exploitation Route These findings are being used in other studies in the area of street lighting and are being discussed in professional and standards forums.
Sectors Aerospace, Defence and Marine,Energy,Transport

 
Description The findings of the research have been discussed within the professional lighting community. They have informed the latest lighting standards and will go on to impact how lighting is designed.
First Year Of Impact 2016
Sector Energy,Environment,Transport
Impact Types Policy & public services