Visual Performance Under Mesopic Conditions: Towards Determination of Adaptation Luminance

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto. fi Author Can Cengiz Name of the doctoral dissertation Visual Performance Under Mesopic Conditions: Towards Determination of Adaptation Luminance Publisher School of Electrical Engineering Unit Department of Electrical Engineering and Automation Series Aalto University publication series DOCTORAL DISSERTATIONS 163/2015 Field of research Illumination Engineering Manuscript submitted 30 April 2015 Date of the defence 13 November 2015 Permission to publish granted (date) 22 July 2015 Language English Monograph Article dissertation (summary + original articles) Abstract The Commission Internationale de l'Eclairage (CIE) published a system for visual performance-based mesopic photometry in 2010. It is valid between the luminances 0.005 cd/m2 and 5 cd/m2. In night-time driving condi-tions, the luminances in the visual scene are in the mesopic range; thus, mesopic photometry should be adopted when assessing lighting in outdoor areas and other night-time traffic environments. In order to implement the CIE mesopic photometry, the background photopic luminance, i.e. ad-aptation luminance, is required as an input value. The aim of the study is to develop methods for estimating the field of view of which the luminance is to be used as the adaptation luminance in implementing the CIE 191 system for mesopic photometry. This is realised by applying methods such as combining eye-tracking data with correspond-ing luminance data and analysing peripheral target detection under uni-form and non-uniform luminous backgrounds. In the study of combining eye-tracking measurements with luminance data, the visual scene areas with the highest density of gaze distributions were determined. The measured luminances for these visual scenes were used to form an estimate of the adaptation luminance under different driving conditions in the lit and the unlit sections of a rural road. The mean luminances of the estimated fields were higher in the unlit section than in the lit section of the route for all drivers. This was due to high-beam head-lights that illuminated the road surface, whereas the gaze points were con-centrated in the unlit section. Experiments in laboratory conditions were conducted in order to obtain the effect of background and target location and its luminance on visual performance. Reaction time and contrast threshold measurements were made to analyse peripheral target detection in uniform and non-uniform backgrounds. Under non-uniform background luminances, peripheral tar-get detection depends on the local luminance of the target and the lumi-nance uniformity of the surrounding area of the target. The results verify that each part of the retina adjusts its sensitivity independently, which re-fers to local adaptation. However, the complexity of the visual field also has an effect on visual sensitivity in peripheral vision. Further studies, where road type, driving speed and discomforting glare are taken into account, are needed to define the visual adaptation field and corresponding adaptation luminance in various driving conditions.The Commission Internationale de l'Eclairage (CIE) published a system for visual performance-based mesopic photometry in 2010. It is valid between the luminances 0.005 cd/m2 and 5 cd/m2. In night-time driving condi-tions, the luminances in the visual scene are in the mesopic range; thus, mesopic photometry should be adopted when assessing lighting in outdoor areas and other night-time traffic environments. In order to implement the CIE mesopic photometry, the background photopic luminance, i.e. ad-aptation luminance, is required as an input value. The aim of the study is to develop methods for estimating the field of view of which the luminance is to be used as the adaptation luminance in implementing the CIE 191 system for mesopic photometry. This is realised by applying methods such as combining eye-tracking data with correspond-ing luminance data and analysing peripheral target detection under uni-form and non-uniform luminous backgrounds. In the study of combining eye-tracking measurements with luminance data, the visual scene areas with the highest density of gaze distributions were determined. The measured luminances for these visual scenes were used to form an estimate of the adaptation luminance under different driving conditions in the lit and the unlit sections of a rural road. The mean luminances of the estimated fields were higher in the unlit section than in the lit section of the route for all drivers. This was due to high-beam head-lights that illuminated the road surface, whereas the gaze points were con-centrated in the unlit section. Experiments in laboratory conditions were conducted in order to obtain the effect of background and target location and its luminance on visual performance. Reaction time and contrast threshold measurements were made to analyse peripheral target detection in uniform and non-uniform backgrounds. Under non-uniform background luminances, peripheral tar-get detection depends on the local luminance of the target and the lumi-nance uniformity of the surrounding area of the target. The results verify that each part of the retina adjusts its sensitivity independently, which re-fers to local adaptation. However, the complexity of the visual field also has an effect on visual sensitivity in peripheral vision. Further studies, where road type, driving speed and discomforting glare are taken into account, are needed to define the visual adaptation field and corresponding adaptation luminance in various driving conditions.