Brightness perception in the mesopic range - models and new laboratory experimentsNils Haferkemper, Stefan Söllner, Dmitrij Polin, Peter Bodrogi, Tran Quoc Khanh, Laboratory of Lighting Technology, Technische Universität Darmstadt , Germany Introduction With every new headlamp technology entering into series production, a new possibility appears that claims to improve visual performance during nighttime driving. To judge such technologies and to generate an objective advance in perception for car drivers, it is crucial to know how the human visual system works under night time driving conditions. In 2010 the TC 1-58 of the CIE published a first “Recommended System for visual performance based mesopic photometry” which is – among others - to be applied for driving a car by night. This CIE approach pictures a unified and simplified model of twilight visual performance. Of course this is a big step forward in photometry, but simplification prevents a deeper description of the visual processes taking place in the mesopic range and thus not giving the chance to optimize additional relevant quantities like ”detection probability” or “feeling of safety”. Visual mechanisms also working in the photopic range behave in a completely different manner when the state of adaptation becomes lower approaching night-time road lighting levels. Another drawback of the CIE model is that it is based only on experiments that took place under simplified laboratory conditions without considering inhomogeneous luminance distributions or age-related pupil size. Typical inhomogeneous luminance distributions are regulated in international standards for vehicle lighting. Mesopic brightness is a different visual function from visual performance related to a relatively slow visual evaluation of relatively large visual fields or the whole environment. It is suspected to be related to the assessment of other visual functions like the state of adaptation, pupil size at the lower stages of vision and also to the feeling of safety at the upper level of human visual information processing. So the authors state thata deep understanding of mesopic brightness is essential for modeling further visual mechanisms. Further the authors believe that a certain mesopic brightness level defines the actual operating point for fast visual performance related mechanisms of human vision hence having influence on visual acuity, detection efficiency, discomfort and disability glare perception, glare recovery time, perceived safety or feeling of safety. It should be emphasized that, although the above mentioned visual functions are related, different models are required to predict them. Also note that currently there is no internationally endorsed model for mesopic brightness. |