Photobiological safety testing and analysis of high-power LED street lights

　　1 Introduction

　　With the continuous advancement of LED technology, LED efficacy continues to increase, and the brightness continues to increase. The era in which LED light would not cause harm to the human body is gone forever. Developed countries and regions such as Europe and North America have begun to pay close attention to the photobiological safety of LED products and have begun to formulate a series of standards. However, the current research on LED photobiological safety testing technology in China is still very weak, and there are very few research papers on related testing systems and methods.

　　This article conducts a photobiological safety test on a high-power LED street lamp that is currently widely used in LED lighting. First, the radiant illumination, radiant brightness, and apparent light source are tested, and finally the hazard types of the test results are analyzed and classified. Since ordinary lighting LED light sources do not produce infrared spectrum above 800nm, this experiment only tests the spectral range of 200nm to 800nm.

　　The basic parameters of the lamp are as follows: voltage 220 V, current 0.3248 A, power 65.98 W, power factor 0.9231, frequency 50 Hz; luminous flux of the lamp is 5747.3 lm, central light intensity 1727.33 cd, maximum light intensity 2839.16 cd, maximum light intensity angle c: 180.0° γ: 59.0°, luminous efficacy 87.11 lm/W, correlated color temperature 4632 K, color rendering index Ra = 69.1, chromaticity coordinates x = 0.3617y = 0.3949 u = 0.2062 v = 0.3378.

　　2 Irradiance test

　　Generally speaking, the light distribution design of LED street lamps is designed according to the needs of road lighting, so the field brightness value obtained at the central axis position of the street lamp is often not the maximum value. The maximum light intensity direction of this sample is: c: 180.0° γ: 59.0°. Considering that the test needs to be carried out in the direction of the maximum hazard of the street lamp, a special fixture is required during the measurement, and the maximum light intensity direction of the fixed lamp is perpendicular to the end face direction of the detector.

　　This experiment uses a spectrum analyzer with a spectrum test range of 200nm to 930nm. Before the irradiance test, the spectrum analyzer should be calibrated first. The experimental setup is shown in Figure 1.

　　Due to the large span of the test spectrum range, the calibration of the spectrum analyzer must use two different light intensity standard lamps for each band. Among them, the standard deuterium lamp with a constant current of 300 mA is used for the calibration of the 200nm ~ 350nm spectrum; the standard halogen tungsten lamp is used as the light intensity standard lamp for the calibration of the 350nm ~ 800nm ​​spectrum signal.

　　The test system uses a mixing ball with a hole as the input port of the detector. The small mixing ball can fully receive the photometric signal in front of the detector. Since the photometric signal has a strong directionality in the measurement of the photobiological safety system, the mixing ball can also make a good cosine correction for the directionality of the lamp under test when fully receiving the photometric signal.

　　In addition, the random reflection of the internal material of the mixing ball will cause the incident light to be polarized. After multiple reflections, the incident light with the same spectral characteristics can fill the radiation incident aperture, thereby avoiding the difference in polarization characteristics of incident light at different angles.

　　After the calibration is completed, remove the light intensity standard lamp, install the LED street lamp to be tested, and measure the radiant illuminance of the sample. Generally speaking, the maximum illuminance used for general lighting is 500 lx, so this illuminance is used for measurement when evaluating general lighting lamps. In addition, the calculation of the hazard value of the light source is to scan the spectrum and then perform a hazard function weighting. The variation of the hazard weighting function of blue light is very large, so the measurement wavelength interval is set to 1nm in this system to ensure the accuracy of the test results.

　　Measure the illuminance value generated by the maximum light intensity angle (C: 180.0° /G:59.0°) of the lamp at the end face of the mixed light ball. Adjust the distance of the lamp to produce 500 lx illuminance at the end face, and fix the distance for spectrum testing. It should be noted that the physiological avoidance distance of the human eye is 200mm. Considering the principle of the worst expected use conditions during the use of the lamp, the test distance must be greater than 200mm.

　　The relative spectral power value of the lamp is obtained under 500 lx illumination, and the measured illumination spectrum distribution diagram is shown in Figure 2:

　　By collecting data through the software, the spectral irradiance test results of the lamps in various bands are automatically obtained:

　　

　　3 Radiation lamp emission limits

　　According to the requirements of GB/T 20145-2006 "Photobiological safety of lamps and lamp systems", the emission limits for continuous radiation lamps within the specified exposure time are shown in Table 1. For non-hazardous lamps, no limit should be exceeded.

　　The brightness test uses an imaging brightness meter of model MPR-16, which has a continuous focus function. Before the brightness test, the brightness meter should be calibrated. The brightness calibration uses a diffuse reflection whiteboard and is connected to the test system, as shown in Figure 3.

　　Since the reflectivity of the reflector can be obtained from the China Institute of Metrology, the brightness value L on the standard white board can be easily obtained from the conversion relationship of illumination brightness. The brightness meter can be calibrated based on the brightness value L.

　　After the calibration is completed, remove the light intensity standard lamp and whiteboard, install the LED street lamp to be tested, and measure the radiant brightness of the sample. Also at the distance of 500 lx illumination and the maximum light intensity angle position C: 180.0° /G: 59.0°, adjust the focal length of the luminance meter so that the luminous surface of the lamp is completely clear on the imaging surface of the luminance meter, measure the radiant brightness value of the lamp, and obtain the average brightness value of the field of view and the brightness spectrum distribution data.

　　Finally, under the same test conditions as the brightness, measure the apparent source brightness distribution of the lamp to obtain the apparent source subtend angle value.

　　Due to the physiological limitations of the eye, the minimum subtended angle of the image on the retina of a stationary eye is 0.0017 radians. When the observation time is greater than 0.25 s, rapid eye movement will blur the light source image, covering a larger area on the retina, forming a larger subtended angle. The subtended angle of the surface light source and the distribution of the light source brightness can be obtained through CCD imaging testing. The exposure parameters of the emitted light in different bands under specific exposure time are tested, and the results are as follows:

　　Then, the apparent source angle to the chord is measured, and the result is:

　　α = 0.041rad

　　4. Analyze and determine various radiation hazard categories.

　　4.1 Analysis of eye hazards caused by photochemical ultraviolet and near-ultraviolet radiation

　　Since the effective integrated spectral illuminance Es and EUVA of the lamp's ultraviolet radiation are both 0, which is less than the standard limit, there is no photochemical ultraviolet and near-ultraviolet hazard.

　　4.2 Analysis of retinal blue light hazards

　　The standard stipulates: In order to prevent retinal photochemical damage caused by long-term exposure to blue light radiation, the blue light weighted radiance LB should not exceed 100W·m-2·sr-1 when the exposure time t of the lamp does not exceed 10000 s.

　　According to the relationship between eye movement and measured opposite angles, the experiment measured that when the exposure time t is 10000s, the corresponding blue light weighted radiance LB is 67.2W·m-2·sr-1, which is less than the standard limit and meets the standard requirement that non-hazardous lamps do not cause blue light damage to the retina within 10000s.

　　4.3 Analysis of retinal thermal hazards

　　The standard stipulates: To prevent retinal thermal damage, the heat hazard weighted radiance of non-hazardous lamps should not exceed the limit when the exposure time t does not exceed 10 s:

　　Substituting the experimentally measured chord angle α = 0.041 rad and t = 10s into the above formula, we can obtain the limit requirement: 28000 /α = 28000 /0.041 = 682926W·m-2·sr-1.

　　The experimental measurement value is 5.91 × 103W·m-2·sr-1, which is less than the standard limit. Therefore, the lamp has no retinal thermal hazard.
 

　　4.4 Retinal thermal hazard exposure limit - analysis of hazard to weak visual stimulation

　　The standard stipulates: For an infrared thermal light source or any near-infrared light source, when observed by the eye and the irradiation time is greater than 10s, its near-infrared (780nm ~ 1400nm) radiance should be limited to:

　　Substituting α = 0.041rad into the formula, we know that the near-infrared radiance limit is 146341W·m-2·sr-1. The experimental measurement value is 0.836W·m-2·sr-1, which is far below the standard limit and therefore meets the requirements for non-hazardous lamps in this project.

　　4.5 Analysis of the hazards of infrared radiation to eyes

　　The standard stipulates: In order to avoid thermal damage to the cornea and sequelae to the lens (such as cataracts), for infrared radiation with a wavelength of 780nm to 3000nm, when the exposure time is less than 1000s, the visual exposure limit of infrared radiation is:

　　Substituting t = 1000s into the formula, the limit value of non-hazardous lamps is 101W·m - 2. The measured experimental value is 1. 40 × 10 - 3W·m - 2, which is far below the limit requirement. Therefore, this lamp has no near-infrared retinal hazard.

　　5. Summary

　　According to the analysis of the above experimental results, and in comparison with the requirements of the standard GB/T20145-2006 "Photobiological Safety of Lamps and Lamp Systems", it can be known that the lamp has no eye photochemical ultraviolet and near-ultraviolet hazards, no retinal blue light hazards, no retinal thermal hazards, no weak visual stimulation, and no eye infrared radiation hazards, and the lamp should be classified as a non-hazardous lamp. This article comprehensively tests the photobiological safety items such as radiant illumination, radiant brightness, and apparent light sources of LED street lamps, and analyzes and discusses the experimental results, which has a certain reference value for the research on the test system and test method of the photobiological safety of LED products.