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According to the difference in the responsiveness of the human eye to the biological effects of different wavelengths of light radiation, in order to improve the lighting comfort, the high-pressure sodium lamp of the highway tunnel common illumination source and the white LEDs of three different color temperatures are respectively used as the only illumination source, in different ambient brightness conditions. Next, the subject's flash fusion frequency value (FFF) for the same scintillation optotype was tested. The statistical results show that the flash fusion frequency corresponding to the same light source is proportional to the ambient brightness. Under the same ambient brightness condition, the flash fusion frequency corresponding to the high pressure sodium lamp is the smallest, and the flash fusion frequency of the high color temperature white LED is greater than the low color temperature white LED. Through the human eye Sichen visual spectral efficiency function and the light source emission spectrum, the "Sichen brightness" which characterizes the degree of influence of human eye photobiological effects is obtained. The value is consistent with the flash fusion frequency test result, and the light source corresponding to the human eye photobiological effect is significant. The greater the frequency of flash fusion, the more effective the effect on fatigue suppression.
The purpose of road tunnel lighting is to provide a better working environment for road users, to improve the efficiency of traffic and reduce the incidence of accidents. The research on highway tunnel lighting design standards has been carried out for a long time in the world. It mainly focuses on the brightness index requirements of different lighting segments. In recent years, with the large-scale application of white LED light sources, the color temperature and color rendering index and other indicators on highway tunnel lighting visibility. The impact has gradually become a hot topic of research.
Under the premise of ensuring safety and visual recognition, improving the comfort of human vision is also an important aspect to evaluate the advantages and disadvantages of lighting sources. Due to the semi-enclosed space characteristics of road tunnels, the visual pressure and monotonous environment are very likely to aggravate the driver's Fatigue and irritability, and the difference in the degree of influence of different light sources on human eye biological effects makes the light source spectrum become one of the research directions affecting the safety of tunnel lighting in addition to the illumination environment brightness.
The impact of fatigue on driving safety
According to the theory of safety behavior, driving behavior belongs to the classic mode of human behavior S-O～R (stimulus-intermediate variable-action). During the driving process, the driver completes the information collection, brain analysis and driving behavior. Driving tasks, in which visual perception is the most important source of information for drivers, can cause traffic accidents if problems occur in any part. Through statistics and related research, drivers are the main factor in many factors that cause traffic accidents, and fatigue driving is one of the main causes of accidents. The causes of driving fatigue include physical and mental effects. The specific characteristics include back pain, blurred vision, slow response, etc., which cause the driver's physiological and psychological functions to be affected to varying degrees, which hinders reasonable driving behavior. Judgment and execution ultimately lead to traffic accidents during driving.
Influence of lighting conditions on flash fusion frequency
Flash Fusion Frequency (FFF)
The human eye is not a perfect imaging system. The external light signal stimulates a certain delay on the retina. When the blinking frequency of the light signal is low, the flicker can be recognized, but as the flicker frequency increases to a certain threshold, The flicker will not be detected, and it will be a stable luminescence in the human eye. The individualized difference of this threshold is large, and it will be affected by the physiological and psychological factors of the subject. The flash fusion frequency characterizes the time resolution of the human eye to non-continuous light stimulation. For the same subject, the FFF is affected by the light source intensity, light color, area, angle of view, age and fatigue of the subject. Impact. As far as the influence of fatigue is concerned, under the same test conditions, as the fatigue of the subject is strengthened, the threshold of the resolvable frequency of the blinking optotype decreases with the human eye. According to this characteristic, the FFF index of the human eye is often used. Test evaluation of the degree of central nervous system fatigue in the brain.
Light source impact test on FFF
This project is based on the flash fusion frequency test of the influence of light environment on the fatigue of the subjects. The test equipment used in the test design phase is different from the conventional flash fusion frequency meter. The main difference is that the flashing point of the test equipment is constant luminous intensity. The white LED does not change the luminous intensity and color of the flashing point during the whole test, and the flashing point is placed in an open test environment. There is no optical black box required by conventional equipment, but the test environment is a strict optical darkroom. In the test phase, the illumination source only has the illumination of the tested, no ambient light and other light sources. The test equipment and test scene are shown in Figure 1:
Before the flash fusion frequency test begins, the subject needs to sit in the lighting environment formed by the test light source for 10 minutes, and then turn on the flash fusion frequency tester. The test is performed in ascending and descending order: the ascending order is from low frequency to high frequency. The frequency is lowered to l0Hz, and then the subject is required to press the trigger button on the instrument to gradually increase the frequency. After the light source is not blinked, press the second button to transmit the current frequency parameter to the upper computer. The descending order is from high frequency to low frequency. First, the frequency is raised to no bright spot flashing. The button on the side of the instrument is pressed to reduce the blinking frequency. When the subject can see the bright spot flashing, stop. frequency. Each test is tested in ascending order, ascending order, ascending order, and descending order. A total of 4 data are tested and the arithmetic mean is taken.
A total of 20 subjects were tested and selected between the ages of 20 and 28, with normal color vision and corrected vision. The ambient lighting source for testing includes high-pressure sodium lamps (color temperature 1958K), high color temperature white LED (color temperature 4765K), medium color temperature white LED (color temperature 4054K), low color temperature white LED (color temperature 3177K), and the selected test environment. Brightness includes, 1 cd/m, 5 cd/m, and 15 cd/m. , 30 cd/m and 50 cd/m, the flash frequency adjustment step is 0.1 Hz.
Analysis of test results
Due to the long duration of the test, the subject is affected by external disturbances during the test, which may cause the test data to seriously deviate from the actual result, and artificially throw away some data that deviate from the mean but not belong to the abnormal value, and will also deviate from the actual result. In view of this, in the data processing process, the results of the multiple repeatability test are determined according to the Layida criterion, and the test result shown in FIG. 2 is taken as an example, and the test result exceeding the allowable range is screened out.
After the data is screened out, the statistical average of the flash fusion frequency test results of the subjects under different light sources and different ambient brightness conditions are shown in Table 1 and Figure 3.
The statistical average of the test results shows that under the same test light source, the flash fusion frequency of the subject increases with the increase of the ambient brightness. Under the same ambient brightness condition, the flash fusion frequency corresponding to the high pressure sodium lamp is smaller than the flash fusion corresponding to the white LED. The frequency, and the high color temperature white LED corresponding to the flash fusion frequency is higher than the low color temperature white LED test results. It shows that the improvement of the ambient brightness helps to improve the driver's visual sensitivity and reduce the fatigue, while the high color temperature white LED has better fatigue relief effect than the low color temperature white LED and the high pressure sodium lamp.
Flash Fusion Frequency Analysis Based on Sichen Vision
Sichen vision is the same as visual perception of dark vision, dark vision and intermediate vision. It is the stress response of human eyes to human light. The difference is that Sichen vision is the melatonin secretion of nerve cells through the action of nerve cells. It does not have visual imaging function, while other visual functions are imaging functions through cone cells and rod cells, but in essence, the response of human optic nerve cells to different wavelengths of radiation, the relationship between wavelength and human eye responsiveness. As shown in Figure 4.
In order to more clearly analyze the influence of different illumination sources on the biological effects of human eye light, the "Sichen brightness" under the visual condition of human eyes is calculated according to the calculation method of bright visual brightness, and the specific data is used to qualitatively represent the different emission spectra. The influence of the illumination source on the biological effects of human eye is calculated as follows:
In the formula, P(A) represents different human visual spectral efficiency functions, which is the normalization coefficient corresponding to the spectral efficiency function. The visual function corresponds to 6831 m/W, and the dark visual corresponds to 17001 m/W. Chen vision corresponds to 38501m/W, and (A) shows the emission spectrum of the incident light source.
The emission spectrum of the high-pressure sodium lamp is characterized by the characteristic line of sodium ion at 589.0 nm and 589.6 nm and its resonance broadening, and the color of the light is yellow. The white LED adopts the double (multi) color mixing of the semiconductor chip illuminating and illuminating the phosphor. The white light is obtained by illuminating, so white light of different color temperatures can be obtained by adjusting the light intensity ratio of the primary color light. The emission spectrum of the test illumination light source is as shown in FIG. 5, and the spectral contours and peak wavelengths of the emission spectra of different color temperature white light LEDs are similar. It is characterized by a bimodal band spectrum, and the double peaks are derived from the blue light emission of the GaN chip (the peak wavelength is about 460 nm) and the YAG:Ce "the excited yellow light (the peak wavelength is about 570 nm), the peak position and the relative intensity are different. This results in a difference in color temperature of the light source.
The spectral efficiency function of the light source and the different spectral efficiency functions of the human eye are substituted into the formula (1), and the four darkness of the test light can be obtained by the calculation. The corresponding dark visual brightness and the Sichen visual brightness index are shown in Table 2. Shown.
Through the calculation of the different light source "Sichen brightness", the calculation result can be obtained: under the same bright visual brightness condition, the "Sichen brightness" value of the high pressure sodium lamp is the lowest, and the "Schenchen brightness" calculation result of the high color temperature white light LED is obtained. Compared with the low color temperature white LED, compared with the test result of the human eye flash fusion frequency, the calculation result of "Sichen brightness" is consistent with the change trend of the human eye flash fusion frequency test result, and the light source with higher "Sichen brightness" is The corresponding human eye flash fusion frequency value is higher, that is, the inhibition effect on human visual fatigue is more obvious.
The main reason for analyzing the test results is that the content of short-wave components in high-color-temperature white LEDs is relatively high, which is in good agreement with Sichen's visual spectral efficiency function, and has a more significant effect on human biological effects. The emission spectrum of high-pressure sodium lamps is basically concentrated in The long wave part has little effect on the biological effects of human eye.
in conclusion
The high-pressure sodium lamp and three white LEDs with different color temperatures are commonly used as illumination sources for highway tunnels. The flash fusion frequency test of human eyes under different light sources and different ambient brightness conditions is obtained: with the increase of ambient brightness, the corresponding flash of different light sources The fusion frequency is increasing; under the same ambient brightness condition, the flash fusion frequency of the high pressure sodium lamp is the smallest, and the higher the color temperature, the higher the flash fusion frequency of the white LED. Through the fitting analysis of the light source emission spectrum and the human eye spectral efficiency function, under the same bright visual brightness condition, the high color temperature white light LED has better short-wave component and better matching with the Sichen visual spectral efficiency function. That is, the inhibition effect on human eye fatigue is more significant, and the visual effect of the high-pressure sodium lamp is the worst, and the analysis result is consistent with the statistical test results. In lighting applications, for the functional requirements of specific lighting projects, in places where non-continuous operation and need to alleviate the fatigue of lighting service objects, it is advisable to use illumination sources with high short-wave components, that is, "Sichen brightness". When measuring at the reference point, there is a certain error in the selection of the measurement range.
When using HDRI to extract brightness, the error is mainly caused by the shooting process, the synthesis process of HDRI, and the difference between the read point of the homebrew software and the test point of BM-7. During the shooting, we used a tripod and shutter release to avoid errors caused by displacement and vibration during shooting, but sometimes there is inevitably a slight displacement during different exposures; using HD Photomatix 4.2 software to synthesize HDRI In the process, you need to use the alignment and de-ghosting functions in the software, which will also cause certain errors. In the process of extracting the brightness information from HDRI, we use the software developed by ourselves, and because of the perspective relationship and the camera. The imaging feature is that the distance from the farther point is smaller on the image, and the point of reading the data is inevitably different from the area measured by the BM-7 chromaticity luminance meter, thereby generating an error. This error is also the main cause of errors in the above experiments.
Conclusion
In order to overcome the deficiencies of LDRI, HDRI is used to obtain optical parameter information, and this paper attempts to establish a method of HDRI for the illumination environment that acquires luminosity parameters. In the road lighting environment test experiment, the method was checked for reliability. Through experiments, the conclusions are:
1) The accuracy of this method is 0.1 cd/m. So for low brightness areas, this method is not applicable.
2) The error rate of the average brightness measured by this method is about 5%. Therefore, the method can more accurately evaluate the overall information of the lighting environment.
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