Stv's Visibility Based On The Small Target Led Street Light Vision Research

The principal purpose of roadway lighting is to produce quick, accurate, and comfortable visibility at night. Usually the truth that night accident rates would decrease and nighttime driver performance would increase with increasing light levels is accepted. This truth is now confronted now, and small target visibility (STV) is more suitable for roadway lighting.A STV experimental was designed, which parameters, such as back ground luminance, contrast, spectrum, duration of target are controlled by computer. With the aid of filter, five monochromatic lights were produced. And the reaction time which are influenced by the spectrum of these lights are record and analyzed. Based on the results of this visual performance experiments, a model for the calculation of threshold luminance was established, which can predict the influence of the relative spectral power distributions of light on the STV. More than that, a similar projector experiment was designed. In this experiment, the background of STV were light by LEDs and HPS, and the reaction time of subject were record and analyzed, then the comparison between LEDs and HPS is made. The result shows that targets are more visible under LEDs illumination conditions than under HPS illumination conditions despite the visibility levels of the small targets are all the same.Now LED has been widely used in roadway lighting because of characteristics such as high efficacy, long life and white light. Because of its luminous distribution is different from other light sources, optic design should be applied to the LED. Different with imaging optics, illumination optics belongs to nonimaging optics. Base on the standard of STV, a new method to design free form reflector was introduced.An in situ field study was conducted to examine the effect of SPD on the ability of detection of small object on the road surface, which it crucial for the safety of the drivers. Comparison between subjective rating in the case of fixed road lighting installation with LEDs and those in the case of HPS lamps was made by using visual experimental data and computer programs. And visual experiments with colored targets were also conduced to study the effect of color on the detection of small object under the road lighting conditions lit by LEDs and HPS lamps.The results of this comparative study show that achromatic and colored targets are a little more visible under LEDs illumination conditions than under HPS illumination conditions despite the visibility levels of the targets are all the same. The LEDs in our study have positive influence on visibility under road lighting conditions, but it is difficult to guarantee the influence is positive because of the diversity SPD of LEDs. The results also suggest if the road is lit by LEDs, colors have an effect on the visibility of object on road surface. This is very important, since color difference will play a prominent role on the detection of hazard object,when the difference between luminance of object and road surface is small,.