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Optical Biological Safety Test and Analysis on High-power LED Streetlights

收藏本信息编号:4319 发布时间:2012-09-10 截止日期: 地区:

Introduction
With the continual progress of LED technology, the power and brightness of LED keep increasing. The time when LED light did no harm to human being has gone. Instead, developed countries in Europe and North America pay more attention to LED optical biological safety and are working out a series of standards.  However, we are still weak in the research on testing technology of LED optical biological safety, and have little available literature on related testing systems and methodology researches.
This article is about an optical biological safety test on high-power LED streetlights largely used in the present LED lighting. First, irradiance, radiance, and apparent light source will be tested, and hazard types of testing results will be analyzed and classified. Since common LED light source will not produce infrared spectrum above 800nm, this test will only cover the spectrum between 200nm ~ 800nm.
The basic parameter of this lamp is as follows: Voltage 220 V, current 0.3248 A, 65.98 W, power factor 0.9231, and frequency 50 Hz; luminous flux 5747.3 lm, central light strength 1727.33 cd, maximum light intensity 2839.16 cd, and maximum light 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.


Irradiance testing
Generally speaking, LED light distribution is designed accordance to the needs of street lighting. Therefore, field luminance value of the central axis of the streetlight usually is not the maximum. The maximum light intensity of this sample is from the direction c: 180.0° γ: 59.0°. In consideration of the test on the maximum hazard direction of the streetlight, special fixtures are used in the testing, and the maximum light tensity of the fixed lamp is perpendicular to the detector end face.
The spectrum testing scope of the radiation spectrum analyzer used in this test is 200nm ~ 930nm. Before the irradiance testing, the radiation spectrum analyzer should be calibrated first. The experimental configuration is sketched in Figure 1 Javascript;
Because of the high-span of the testing spectrum, two luminous intensity standard lamps are used for calibration of the radiant spectrum analyzer. The standard deuterium lamp supported by constant current 300 mA is used for 200nm ~ 350nm spectrum calibration, and the standard halogen tungsten lamp as the luminous intensity standard lamp is adopted for 350nm ~ 800nm spectral signal calibration.
Mixed photosphere opening is adopted in the testing system as the input port of the detector. The small photosphere can fully receive the intensity signal before the detector. For the strong directivity of the intensity signal in optical biological safety testing, the mixed photosphere can not only fully receive the intensity signal, but also make good cosine correction on the directivity of the tested lamp.
Besides, polarization of the incident light will occur in the random reflection of the interior material of the mixed photosphere. Incident light of such spectrum will fill the input port after many times of reflection, so that the difference on the polarization of incident light from different angles can be avoided.
After calibration, the luminous intensity standard lamp is removed, and the LED streetlight to be tested is installed for radiance testing. Generally speaking, the maximum luminance of the common lighting is 500 lx. Therefore, this luminance is adopted in the testing for the assessment of common lamps. Besides, the hazard value of light source is the hazard weighting function after spectrum scanning. There are large changes in the hazard weighting function of the blue light. Therefore, the interval of the testing wavelengths in this testing system is 1nm to assure the accuracy of the testing results.
The testing direction of the maximum light angle of the lamp is (C: 180.0° /G: 59.0°) on the luminance produced on the end face of the mixed photosphere. The distance of the lamp is adjusted so that the end face can produce 500lx luminance. The distance is fixed for spectrum testing. It should be noted that phycological collision distance of human eyes is 200mm. In consideration of the principle of the predicted worst conditions in lamps, the testing distance should be larger than 200mm.
Correlated spectral power values of the lamp is obtained under 500 lx luminance. The tested luminance spectrum distribution is sketched in Figure 2:
Data is automatically collected by software, and irradiance testing results of different wavelengths are as follows:


Emission limit of radiant lamps
In accordance with GB /T 20145—2006 Optical Biological Safety of Lamps and Lighting Systems, emission limit of continual radiant lamps within a fixed radiation period is sketched in Figure 1. No non-hazard lamp should exceed any of the limiting values.
In luminance testing, MPR-16 imaging luminance meter is adopted. The meter has continual focusing function. Before luminance testing, the luminance meter should be calibrated first. Diffuse reflection white board is used in luminance calibration. The connection testing system is sketched in Figure 3.
The standard reflectivity data of the reflection board can be accessed in National Institute of Metrology. The luminance value L of the standard white board can be easily obtained from the transformational relations of luminance. The calibration of luminance meter can be finished in accordance with luminance value L.
After calibration, the luminous intensity standard lamp and the white board are removed and the LED streetlight to be tested is installed for radiance testing. Under the same condition of 500 lx luminance distance and the maximum light angle C: 180.0° /G: 59.0°, the focus of the luminance meter is adjusted so that the luminous surface of the lamp can clearly produce its image on the luminance meter. The radiance value of the lamp is tested to obtain field average luminance values and luminance spectrum distribution data.
Finally, under the same conditions of luminance testing, the apparent light source distribution of the lamp is to be tested to obtain the chord angle value of the apparent light source.
Because of the psychological limits of eyes, the minimum subtense angle of the image on retina is 0.0017 radian. When the observation time is larger than 0.25 s, instant eye movement will blur the light source image, cover larger area of the retina and form a larger subtense angle. Apparent light source subtense angle and light source luminance distribution can be obtained through CCD imaging testing. The radiation parameter of different wave bands should be obtained in fixed radiation period. The results are as follows:


The analysis and judgment of types of radiation hazards
The analysis on photochemical UV and near UV hazards
Since the effective integrating spectral irradiance of UV radiation, Es and EUVA are 0, lower than the standard limiting value, this lamp has no photochemical UV and near UV hazards.


Hazard analysis on blue light against retina
The standard: In order to avoid photochemical damage to retina for long-term exposure to blue light, when the radiation time t is not larger than 10000 s, the blue light weighted radiance LB should not exceed 100W·m - 2·sr - 1.
In accordance with the relationship between eye movement and the measured subtense angle, when the tested radiation time t is10000s, the corresponding blue light weighted radiance LB is 67.2W·m - 2·sr - 1, lower than the standard limiting value. Thus the lamp conforms to the standard that non-hazard lamps should not do any blue light hazard to retina within 10000s.


The analysis on Thermal hazard against retina
The standard: In order to avoid any damage to retina, when the radiation time of non-hazard lamps is no larger than 10s, light source thermal hazard weighted radiance should not exceed the limiting value:
The tested value is 5.91 × 103W·m - 2·sr - 1, smaller than the standard limiting value. Therefore, this lamp does no thermal harm to retina.


Retinal thermal hazard radiation limiting value— hazard analysis on weak visual stimulation
The standard: As to an infrared light source or any near infrared light source, when the eye observation and radiation time is larger than 10s, the near infrared (780nm ~ 1400nm) radiance should be limited to:


Hazard analysis on infrared radiation against eyes
The standard: In order to avoid thermal hazard against cornea and the crystal sequela (cataract, for example), when the exposure time is less than 1000s, the visual radiation limiting value of infrared radiation, whose wavelengths are between 780nm ~ 3000nm,.

Conclusion
According to the above testing results analysis and the standard GB /T20145—2006 Optical Biological Safety of Lamps and Lighting Systems, it is known that this lamp does not have photochemical UV and near UV hazards against eyes, blue light hazards against retina, thermal hazards against retina, weak visual stimulation, or infrared radiation hazard against eyes. Therefore, this lamp is classified as non-hazard lamps. This article is about a comprehensive test on optical biological safety subjects of LED streetlights, such as irradiance, radiance and apparent light source, as well as an analysis on the testing results, which is valuable for the researches on testing systems and testing methodologies of LED products' optical biological safety.

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