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

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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.