Pedestrian Areas Lighting Evaluating Method Under Mesopic Light Levels

This work is carried out as part of the National High Technology Research and Development Program of China (863) (No.2011AA03A113) and the National Basic Research Program of China (973) (No.2010CB734102).The purpose of road lighting is to provide acceptable visual environment for the drivers and pedestrians, which ensures the traffic safety, helps the end users to discriminate the correct direction and decreases the nightly crime rate. With the development of the traffic construction, the energy demand and cost of road lighting are increasing. In road lighting, the visual system is operating in the mesopic range. The purpose of the thesis is to suggest an evaluation method for road lighting based on mesopic photometry and provide theoretical support for energy saving design in road lighting.The thesis firstly introduced the situation that the energy cost became larger in road lighting because of the rapid development of traffic construction and unreasonably lighting design. The energy saving in road lighting is becoming an urgent problem in China. Afterwards, mesopic vision and MES-2 mesopic photometry system (CIE Recommended System for Mesopic Photometry) was described. For the road lighting in pedestrian areas, where the illuminance was relatively low, one route to reducing energy consumption was by choice of lamp spectral power distribution (SPD) of the light sources.To apply the MES-2 mesopic photometry system to road lighting, it’s necessary to make sure that lamp SPD affects the visual performance of drivers and pedestrians. Thus, the thesis reviewed the existing researches focused on the visual performance of drivers and pedestrians in road lighting and concluded the key visual tasks of drivers and pedestrians. The influence of SPD on visual tasks of pedestrians was analyzed. When it goes to facial recognition, the results of past studies are mixed, with some studies suggesting a significant of SPD on the facial recognition while others do not. In order to apply the mesopic photometry, the photopic luminance of the visual adaptation field of drivers was needed. Up to now, definition of the driver’s visual adaptation field is not clear, so it’s still inappropriate to apply the MES-2 system to road lighting for drivers. Thus, this thesis focused on the pedestrian areas lighting evaluation method.To suggest a lighting evaluation for pedestrian areas, the prior and urgent work was to investigate the effect of lamp SPD on facial recognition. To achieve this and also to investigate why different studies have found different conclusions regarding the effect of lamp SPD, experiments about facial recognition was carried out, using the two different procedures used in past work, three light sources with different SPD, and two observation duration. The results demonstrated the influence of task difficulty on the influence of SPD:if the recognition task was difficult (small visual size and brief observation), it was more likely that lamp SPD would have an effect, on the contrary, if the recognition task was very easy, the effect of SPD was not significant. The task difficulty includes factors such as observation duration and distance. In order to further explore the factors influencing the task difficulty, extra experiments was carried out in the laboratory, with task difficulty varied as five levels of observation duration (0.1 to 10 s), three luminances (0.1 to 10 cd/m2) and two procedures (matching and identification). The results showed that the observation duration, target luminance, recognition procedures as well as the observation distance were all key factors influencing the task difficulty. Thus, according to the results of the experiments based on visual ergonomics, conclusions can be draw that lamp SPD has significant effect on the facial recognition.In consequence, lamp SPD does affect the visual performance of pedestrians, it’s logical to apply the MES-2 mesopic photometry system to road lighting. At the final part of the thesis, the evaluation method for road lighting referring to different SPDs, luminance and road types was setup for drivers and pedestrians respectively. This evaluation method can provide theoretical support for the energy saving in road lighting by reasonably decreasing the demand of the illuminance or luminance in the premise of ensuring the visual performance of the end users.