Photobiosafety Testing and Analysis of High Power LED Street Lamps

1 Introduction With the continuous advancement of LED technology, LED efficacy continues to increase, brightness continues to increase, the era of LED emission from the past will not cause harm to the human body is gone forever, Europe, North America and other developed countries and regions have begun to close Concerned about the issue of photobiological safety of LED products and set out a series of standards. However, at present, the research on LED light bio-safety testing technology in China is still very weak, and there are few research papers on related test systems and methods.

This article examines the bio-optical security of a high-power LED street light that has been heavily used in LED lighting. First, the illuminance, radiance, and surface tourism sources were tested. Finally, the types of hazards were analyzed and classified. Because the LED light source for general lighting does not generate an infrared part of the spectrum above 800 nm, this experiment was only performed on a part of the spectral range from 200 nm to 800 nm.

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 fixture 5747.3 lm, central light intensity 1727.33 cd, maximum intensity 2839.16 cd, maximum intensity Angle c: 180.0°γ: 59.0°, light efficiency 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 In general, the light distribution design of LED street lamps is designed according to the road lighting needs, so the brightness value of the field of view acquired from the central axis of the street lamp is often not the maximum value. The direction of the maximum light intensity of the sample is: c : 180.0° γ: 59.0°. Considering that the test needs to be done in the direction of the maximum hazard of the street lamp, special fixtures are used for measurement. The maximum light intensity of the fixed fixture is perpendicular to the direction of the detector end face.

In this experiment, the spectroradiometer was used to measure the spectrum from 200nm to 930nm. Before the irradiance test, the spectral analyzer should be calibrated for calibration. The experimental setup is shown in Figure 1.




Due to the large span of the test spectrum, the calibration of the spectrum analyzer must be performed in two different intensity standard lamps. Among them, a standard xenon lamp with a constant current of 300 mA is used for spectrum calibration at 200 nm to 350 nm, a spectrum signal at 350 nm to 800 nm is calibrated, and a standard halogen lamp is used as a standard intensity lamp.

The test system uses the method of mixing light bulbs as the input port of the detector. The small light mixing sphere can fully receive the photometric signal in front of the detector. Because the directionality of the photometric signal is strong in the measurement of the photobiological safety system, the mixed light ball When the photometric signal is fully received, a good cosine correction can be made to the directionality of the lamp under test.

In addition, the random reflection of the internal material of the mixed ball causes the incident light to be polarized. After multiple reflections, the incident light with the same spectral characteristics can be filled with the entrance aperture of the radiation, thereby avoiding the difference in the polarization characteristics of the 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 irradiance of the sample. Under normal circumstances, the maximum illumination used for general illumination is 500 lx, so this illumination is used to measure when evaluating general lighting lamps. In addition, the hazard value of the light source is calculated by weighting the hazard function after the spectral scanning. The variation of the hazard weighting function of the blue light is very large. Therefore, the measurement wavelength interval is set to 1 nm in this system to ensure the accuracy of the test results.

Measure the illuminance value of the luminaire at the maximum light intensity angle (C: 180.0°/G: 59.0°) in the direction of the end face of the mixing sphere. Adjust the distance of the luminaire so that the illuminance of the end face is 500 lx, and fix the distance to perform the spectral test. It is necessary to pay special attention to the physiological avoidance distance of the human eye is 200mm, taking into account the expected use of the lamp in the worst use of the principle, we must ensure that the test distance is greater than 200mm.

The relative spectral power of the luminaire is obtained at a illuminance of 500 lx. The measured illuminance spectral distribution is shown in Figure 2:




Through software acquisition data, the spectral irradiance test result of the luminaire in each band is automatically obtained:




3 Emission limit of radiant lamps According to the requirements of GB/T 20145-2006 “Optical biosafety of lamps and lamp systems”, the emission limits of continuous radiant lamps within the specified exposure time are shown in Table 1, for non-hazardous classes. Luminaires should not exceed any limit.




The brightness test uses an imaging brightness meter model MPR-16, which has a continuous focusing function. Before the brightness test, the calibration of the luminance meter should be corrected first. The brightness calibration uses the diffuse whiteboard method to connect the test system, as shown in Figure 3.




Because the reflectivity of the reflector can be obtained from the China Institute of Metrology, the brightness value L on the standard whiteboard can be easily obtained from the conversion relationship of luminance. According to the luminance value L, calibration of the luminance meter can be completed.

After the calibration is completed, remove the light intensity standard lamp and the whiteboard, install the LED street lamp under test, and measure the radiance of the sample. Similarly, at a distance of 500 lx illumination and at a maximum light intensity angle C of 180.0°/G:59.0°, the focal length of the luminance meter is adjusted so that the light emitting surface of the lamp is completely clear on the imaging surface of the luminance meter. The radiance value of the luminaire obtains the average brightness value of the field of view and the brightness spectral distribution data.

Finally, under the same test conditions as the brightness, the brightness distribution of the source of the sightseeing source of the luminaire is measured, and the value of the source angle of the sightseeing source pair is obtained.

Due to the physiological limitations of the eye, the minimum diagonal angle of the image on the retina of the resting eye is 0.0017 radians. When the observation time is greater than 0.25 s, fast eye movements will make the light source appear fuzzy, covering a larger area of ​​the retina, forming a larger angle of the opposite corner, through the CCD imaging test to obtain the light source and the corners and Light source brightness distribution. Test the exposing radiation parameters of the exit light in different band regions at a specific exposure time. The results are as follows:




Afterwards, measuring the source of the table for the chord angle results in:

α=0.041rad

4 Analysis and determination of various types of radiation hazards.

4.1 Eye photochemistry UV and near-ultraviolet hazards analysis Because the ultraviolet radiation of the lamp effectively integrates the spectral illuminance Es, EUVA all 0, less than the standard limit, so no photochemical UV and near ultraviolet hazards.

2 The retinal blue light hazard analysis standard stipulates that in order to prevent retinal photochemical damage to the retina from long-term exposure to blue light, the blue light weighted radiance LB should not exceed 100 W·m-2·sr in case the lamp exposure time t does not exceed 10000 s. -1.

According to the eye movement and the relationship between the measurement and the corners, when the measured exposure time t is 10000s, the corresponding blue light weight radiance LB is 67.2W·m-2·sr-1, which is less than the standard limit value, and no risk is found in the standard. The class lamp does not pose a hazard to the blue light of the retina within 10,000 s.

4.3 Retinal Heat Hazard Analysis Standards stipulate: to prevent retinal heat damage, the hazard weighed radiance of light source heat hazard should not exceed the limit when the exposure time t does not exceed 10 s.




The experimentally measured chord angle α = 0.041 rad, t = 10s is substituted into the above formula, and the limit value required is: 28000/α=28000/0.041=682926W·m-2·sr-1.

The experimental measurement was 5.91×103W·m-2·sr-1, which was less than the standard limit, so the lamp had no retinal heat hazard.

4.4 Retinal Heat Hazard Exposure Limits - Hazards to Weak Visual Stimulation Analysis Standards: For an infrared heat source or any near-infrared light source, when observed with the eye and the irradiation time is greater than 10 s, the near infrared (780 nm~ 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 is 0.836W·m-2·sr-1, which is far below the standard limit, so it meets the requirements of the project for non-hazardous lights.

4.5 Analysis of hazards for infrared radiation of the eyes: Standards: In order to avoid thermal damage to the cornea and sequelae of the lens (such as cataracts), for infrared radiation at a wavelength of 780 nm to 3000 nm, the visual radiation of infrared radiation when the irradiation time is less than 1000 s The limit is:




Substituting t=1000s into the formula, the limit for non-hazardous lights is 101W·m-2. The experimental value measured is 1.40×10-3W·m-2, which is far below the limit value, so the luminaire is free of near-infrared optic retinal hazards.

5. Summary According to the analysis of the above experimental results, in contrast to the requirements of the standard GB/T 20145-2006 “Light bio-safety of lamp and lamp system”, it can be known that the lamp has no photochemical ultraviolet and near ultraviolet hazards, no retina blue light damage, no retinal fever Harmful, no weak visual stimuli, no eye radiation hazards, should be classified as non-hazardous lamps. This article has comprehensively tested the photobiological safety items such as the illuminance, radiance, and source of sightseeing of LED street lamps, and analyzed the experimental results. It has certain research on the test system and test methods for the photobiological safety of LED products. The reference value.