Meri Viikari

Mesopic models : from brightness matching to visual performance in night-time driving: a review

At present, suitable methods to evaluate the visual effectiveness of lighting products in the mesopic region are not available. The majority of spectral luminous efficiency functions obtained to date in the mesopic range have been acquired by heterochromatic brightness matching. However, the most recent studies in the mesopic field have adopted a task performance-based approach. This paper summarizes the major mesopic models proposed so far, presenting in detail the experimental conditions of these studies. The authors represent a research consortium which has adopted the task performance-based approach for night-time driving in which mesopic visual performance has been divided into three subtasks. Data for each sub-task will be generated by using a set of common parameter values and 120 observers. The approach and methods used by the consortium are presented.

Modeling spectral sensitivity at low light levels based on mesopic visual performance.

The spectral sensitivity of the eye at low light levels, ie, mesopic conditions, is determined by the rod and cone photoreceptors of the retina operating together in varying degree as adaptation luminance shifts between the scotopic and photopic. Thus mesopic spectral sensitivity is different from photopic, where only cones contribute to vision. There are definite needs for a practical system of mesopic photometry to be used in assessing light at low light levels, especially in road and other outdoor lighting applications. However, neither of the recently proposed systems of mesopic photometry, the MOVE-model or the X-model, is found satisfactory by common consent of the lighting community. The most active debate has considered the upper luminance limit of the mesopic region, which is regarded to be too high for the MOVE-model and too low for the X-model. The present paper proposes a new modified MOVE-model whose upper luminance limit is adjusted to meet the actual road and street lighting luminance values measured in different weather conditions. The paper compares the MOVE-model, X-model, and the proposed modified MOVE-model with three independent visual performance data sets provided by different European universities. Based on the comparison, recommendations are given for future actions towards internationally accepted practice for mesopic photometry.

Road lighting in change: User advice for designers

Road lighting practice in Europe is currently under change, the changes being induced by the European Union Ecodesign regulations, the rapid development of LEDs and the new CIE system of mesopic photometry. This makes it a good time to listen to the opinions of the end users of road lighting. What are the aspects of road lighting that the drivers value? What are the most difficult visual tasks faced by drivers at night? Are drivers willing to reduce the amount and quality of lighting to save energy? All these questions and more were presented to over 100 drivers aged 20–79 years in a questionnaire in Finland during the autumn of 2010. This paper summarises the results and discusses the expectations of drivers that should be considered when preparing future guidelines for road lighting.

Authors’ response to SA Fotios

three sub-tasks: can it be seen, how quickly, and what is it. This provides a useful framework for devising the experimental work. Would the authors please confirm whether the proposed reaction time tests will be onaxis, off-axis, or both. Also, it is noted several times that their work will use 120 observers: is this particular quantity significant, and if so, why? I look forward to reading the results of the experimental work described in this paper.