In order to give a more reasonable road lighting design standard, American scholars in the United States road lighting standard (RP- 8- 00) suggested that the small target visibility design standard , and given the small target visibility design different types of roads and pedestrian intersection area of the standard value. (as shown in Table 1).
The values in Table 1 are derived from experiments with normal vision of a 60 year old driver, and from a small target size of 0.18 m@ to 0.18 m, with a light reflectance of at least 0.5 and an observation time of 0.2 s on an open Lane Road experiment. It can be seen from table 1: pedestrian intersection area is large value, and low for small value; small target visibility of trunk road was greater than or equal to the value of the high-speed road, this is because determine the visibility of road lighting level not only depends on the type of the road and the traffic flow, but also depends on the complexity of traffic and the separation of traffic status and traffic control, which is according to the actual situation of the road. In the calculation of small target visibility, we must first consider the adaptation surface brightness, target background brightness, eye effect level and equivalent brightness, but also the source of effectiveness, the observation time (reaction time), the driver age and negative contrast correction. The so-called negative contrast correction refers to the occurrence of bright background observation dark target situation in road lighting conditions under actual will, the human eye is not easy to detect bright background of dark target, so be on the threshold of the so-called negative contrast correction. When calculating the weighted average value of the visibility of the small target, that is, when calculating the visibility of the small target, it is to calculate the weighted average value of the small target visibility level respectively after the grid points are calculated. Such as the use of this method, then the visibility of the small target in the connotation of the road all the information the brightness uniformity of the total; in addition, if the background is not only the average brightness of road surface, but also the garage band width of 5 m in the outside edge of average brightness value, then to calculate the value of the existing environment than in the small target visibility (SR) contribution.
For large traffic flow, traffic separation and control situation of poor road, in the night, a person or animal may cross the road, the center of the field goal may deviate from the driver, the original observation for preventing accidents is very important. This vision is called peripheral vision, which is mainly made of rod photoreceptor cells. Peripheral vision plays a decisive role in the detection of moving targets and the evaluation of the distance from the edge of the line. Because the road side of the sidewalk brightness is always less than the average road surface luminance value, so the human vision will not only have the efficiency of cone photoreceptor cells and rod photoreceptor cells in the spectral luminous differences, but also have the human eyes and dark adaptation problems. To this end, we must carry out the pupil brightness and equivalent brightness correction , that is, in the calculation of small target visibility should be the first target brightness and background brightness, etc.. Because usually in road lighting calculations, is in the bright visual conditions, with cone photoreceptor cells in about 2b in the field of view by the flashing of the background color of the measured spectral luminous efficiency function value as the standard, and its peripheral vision is different from that at this time, the road lighting light source spectral distribution different will have great influence on the size of the 3] [correction coefficient, in order to ensure the safe operation, must carry out effective light source. In addition, because in determining the visibility of the small target, is obtained in the observation time was 0.2 seconds, so when the spectral composition of light sources on road lighting and human adaptation is at the same time, the driver saw obstacles and respond to the time required for the so-called reaction time will change. If the time is less than 2 seconds, then it will have an impact on the resolution of the human eye, and visibility will be reduced with time shortened. In order to enable the driver to run safely on the expressway, the correction of the influence of the different composition of the light source spectrum on the reaction time should be increased in the correction coefficient of the observation time, that is to say, to increase the reaction time.
In a word, under the condition of motor vehicle road lighting, small target visibility is an objective measure of human visual function. At night, the driver wants the road fixed lighting system not only to provide good visibility, but also to meet the driver's visual comfort requirements. The main factors that affect the driver's visual comfort are the discomfort glare, the longitudinal uniformity and the induced effect. The discomfort glare and longitudinal uniformity, through the subjective evaluation of a large number of road lighting and calculation, gives the corresponding quantitative glare control level G and longitudinal uniformity of Ul standard; but for the evaluation of this induced an important road lighting quality indicators, both for the optical induced evaluation still, for visual guidance in road lighting design evaluation, the existing methods are not suitable to using quantitative parameters. For this reason, it is suggested to adopt a new method of road lighting design, that is to say, the digital lighting design method (4]) should be used to conduct the quantitative evaluation.
After decades of unremitting efforts, in space science and technology and geographic information system (GIS) technology, remote sensing (RS) technology, global positioning system (GPS) technology on the basis of research results, put forward the concept of digital earth and digital city, it is the crystallization of human wisdom. Virtual reality technology in the digital city road lighting is the true 3D real-time rendering of the scene into the road lighting, is built (structure) terrain, buildings, roads, trees, bridges and other models in real-time 3D modeling of special software (such as Multigen Creator) and three dimensional real time driven simulation software Vega at the same time, aerial photos and satellite or directly with digital camera photos and other building texture and 3D model together, to obtain realistic scene of road lighting.
In order to ensure traffic safety, the need to ensure that the road lighting facilities and with the induction of good, it should be in the virtual reality environment, using Vega software through the graphical interface, the definition of road lighting simulation scene, real-time roaming in the specified road and traffic, road center line, the correct evaluation of road edge stone, lampposts, lamp etc. visual induction, as well as the evaluation of road lighting lighting, color transform and pole arrangement of optical induction of good and bad, objectively judge the road lighting design for many drivers and on roads, linear and gradient information, but also the corresponding semantic differential scale questionnaire and statistical methods based on virtual reality in the environment, the induction of the qualitative evaluation of road lighting facilities and the results into the quantitative evaluation results, so as to correctly guide road lighting design Meter.
In short, the design method of digital city road lighting design, not only can the driver's visual function and visual comfort of the physiological and psychological needs influence the quantitative calculation of the virtual environment but also in the digital city lighting, according to the design standard of road lighting, road lighting design is more reasonable.
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