Browsing by Author "Cengiz, Can"

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Age-related factors on vision at low light levels
(2012) Cengiz, Can
School of Electrical Engineering | Master's thesis
Visual Performance Under Mesopic Conditions: Towards Determination of Adaptation Luminance
(2015) Cengiz, Can
School of Electrical Engineering | Doctoral dissertation (article-based)
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 conditions, 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. adaptation 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 corresponding luminance data and analysing peripheral target detection under uniform 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 concentrated 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 target detection depends on the local luminance of the target and the luminance uniformity of the surrounding area of the target. The results verify that each part of the retina adjusts its sensitivity independently, which refers 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.