1 Overview
The blue light hazard of LED has been controversial, and it has once become a restrictive issue for the promotion and application of LED lighting products, which has affected the consumer confidence of the market. In the eighth edition of the revision of IEC 60598-1 "Luminaires-Part 1: General requirements and tests", the marking requirements for blue light hazards of LED lamps are highlighted. This standard is the basic requirement for luminaires and is cited by most countries and regions in the world. China corresponds to the mandatory standard GB 7000.1. The revision and release of this standard indicates that the classification of the blue light hazard will become a mandatory requirement for LED luminaires. Therefore, it is necessary for LED light source and luminaire manufacturers to take effective detection methods based on relevant standards to measure and evaluate the blue light hazard of products.
2. LED blue light hazard classification and marking requirements
2.1 related standards
LED blue light hazard measurement and evaluation standards mainly include IEC/TR 62778 and IEC62471, IEC 62471-2, etc. IEC 60598-1 adopts IEC/TR 62778 "Application of IEC 62471 for the assessment of blue light hazard to light sources and luminaires ". IEC / TR 62778 IEC 62471 is based on the evaluation of the measuring light and the blue light hazard lamps made simplified. Considering that the LED industry chain is long, and from LED chips to LED lamps, from the upstream to the downstream of the industry, the types of products are becoming more and more abundant. To reduce the test burden, IEC/TR 62778 recommends LED blue light hazards to be transmitted from the light source to the lamps. Evaluation method.
Grading 2.2 LED blue light hazard
In the IEC 62471 standard, photobiosafety is divided into four levels, and the hazard levels from RG0 to RG3 are increased step by step. Among them, RG0 and RG1 are considered to be safe for general applications.
IEC/TR 62778 has been analyzed to find that the general white light source is unlikely to be RG3, and at the same time, to achieve the transmission of the hazard level from the light source to the luminaire, it is redefined as the following three safety levels.
Wherein, "Ethr for RG2" applies to blue light hazard weighted radiance limit or may exceed the radiance RG1 unpredictable situation, EthR illuminance RG1 and RG2 boundary value for determining the hazard limit distance Dmin, the lamp should generally Use outside of this distance.
2.3 Safety requirements for LED luminaires
The standard IEC 60598-1 edition 8 specifies that if the RG0 or RG1 source in IEC/TR 62778 is installed in the luminaire, or if the luminaire is rated RG0 or RG1 under actual application conditions, there is no additional marking requirement. However, children's night lights installed with portable luminaires and power outlets must have a light source that does not exceed RG1. For other integrated LED luminaires, portable luminaires and fixed luminaires, IEC 60598-1 has different marking requirements. For portable luminaires that exceed RG1 under the measurement conditions of 200 mm and 0.011 rd, a warning sign "Do not look directly at the light source" is required. For fixed luminaires, the luminaire shall be evaluated for its minimum safe use distance dmin and the luminaire RG1/RG2 boundary in accordance with IEC/TR 62778. When dmin is greater than 200 mm, the minimum safe use distance is identified.
3. Measurement and evaluation of LED blue light hazards
Standard IEC 62471 and IEC/TR 62471-2 measure and evaluate the radiation hazard of a single light source or luminaire. The difference is that IEC/TR 62778 emphasizes the transmission of blue light hazard information from the source to the luminaire, the main measuring source, and also for direct measurement of luminaires. The measurement evaluation process is shown in Figure 1.
If the light source manufacturer can provide the brightness, radiance and Ethr of the light source (obtained by spectrometry), the luminaire manufacturer can safely classify the luminaire according to the data provided by the light source manufacturer according to the flow of Figure 1, and if necessary, illuminate the illuminance of the luminaire. Here, the illuminance measurement needs to first determine the maximum light intensity direction of the luminaire according to the light intensity distribution information of the luminaire. If the hazard information of the light source is unknown, the luminaire manufacturer needs to measure the brightness, spectrum and other information of the luminaire to classify the hazard level of the luminaire.
3.1 LED blue light hazard measurement points
The LED blue light hazard examines the photochemical damage that blue light produces on the retina. In practical applications, people may look at different areas of the light source or the illuminating surface of the luminaire from different angles. Therefore, in order to meet various applications, IEC 62471 stipulates that the blue light hazard should be classified according to the exposure value (weighted irradiance and weighted radiance) in the direction of maximum radiation intensity of the maximum luminance region of the light-emitting surface.
IEC/TR 62778 mainly specifies the transmission of blue light hazard between the light source and the luminaire. Compared with IEC 62471, the requirements for measuring position are more stringent, and the maximum radiant intensity of the brightness measurement should be emphasized in the maximum brightness area of ​​the light source or luminaire. The direction is measured, and the minimum safe use distance dmin of the luminaire needs to be measured in the direction of the maximum luminous intensity of the luminaire.
In practical applications, the brightness of the light-emitting surface of the light source and the light intensity in each direction of the space are generally not uniform. Taking the LED array shown in FIG. 3 as an example, the brightness on the chip is high, and the gap between the chips is low. Therefore, the determination of the maximum brightness area on the LED illumination surface is critical. If the positioning is not accurate, it will have a great impact on the measurement of brightness and radiance and the classification of hazards. However, due to the characteristics of the LED itself, the maximum brightness area on the light-emitting surface and the accurate positioning of the maximum radiation intensity direction have certain difficulties.
3.2 LED blue light hazard brightness and radiance measurement
If the aiming point type brightness meter is used for measurement, the maximum exposure position is difficult to accurately locate, and the general aiming point type brightness meter is difficult to accurately achieve the standard 0.011rd field of view angle. Therefore, the imaging luminance meter is an ideal measuring device for the brightness and radiance measurement of LED blue light hazard. As shown in Figure 2, the imaging luminance meter has the following advantages:
1) Imaging the surface of the object to be measured to the CCD by one measurement, and its own professional software can automatically and accurately determine the position of the maximum brightness in the imaging area;
2) Measuring the angle of view (the range of the red circle) can be conveniently set by software. As shown in Figure 3, the software automatically calculates the average brightness/radiance within the selected field of view and classifies the blue light hazard according to standard requirements.
Compared with the general ordinary imaging luminance meter, the device shown in Figure 2 uses a high-precision TE-cooling semiconductor cooled CCD as a detector, which can thermostat the operating temperature of the CCD to 5 °C, greatly reducing the measured dark noise and improving the brightness. / Measurement accuracy of radiance, especially suitable for blue light hazard measurement with high accuracy requirements.
3.3 Spectral measurement of LED blue light hazard
The spectrum of the light source or luminaire is an important parameter for calculating the magnitude of the blue hazard. According to the standard, for a certain light source, the blue light hazard efficiency coefficient KB, V can be calculated by spectral measurement, and the formula is as follows:
The acquisition of KB, V can conveniently realize the conversion of luminance L and blue light hazard-weighted radiance LB, and illuminance E and blue light hazard-weighted irradiance EB. The illuminance limit Ethr at the RG1 and RG2 boundaries described in the standard is also calculated therefrom.
The wavelength range of the spectral measurement should cover the sensitive area of ​​the blue light hazard, ie 300nm-700nm; considering that most of the LED products do not have an ultraviolet spectrum, the visible spectrum spectrometer can also be used for the blue light hazard measurement of LED products.
3.4 Integrated solution for LED light source and luminaire blue light hazard measurement
Figure 5 shows the comprehensive test system for the blue light hazard of the light source and the luminaire. The system integrates the high-precision imaging luminance meter and the high-precision spectral radiometer shown in Figure 3, which can accurately realize the hazard-weighted radiance, brightness and hazard of the light source and the luminaire. Measurement of weighted irradiance, illuminance, spectrum, KB, V and Ethr parameters.
The system uses a high-precision imaging luminance meter to accurately find the maximum brightness area of ​​the light source or the illuminating surface of the luminaire. Its unique five-dimensional position adjustment system can move up and down, left and right, back and forth, and can rotate around its vertical and horizontal axes. In the case where the high-precision imaging luminance meter is fixed, the maximum radiation intensity direction of the maximum luminance region on the light-emitting surface of the LED product can be conveniently located with high accuracy and good reliability.
1) Measurement of LED light source
The light source is mounted on a five-dimensional position adjustment system. After determining the maximum exposure position of brightness and radiance, the system can sequentially align the light source with the measuring device, and test the brightness, radiance, and spectral data of the light source to be automatically calculated. The blue light hazard-weighted radiance LB and Ethr, and the blue light hazard classification of the light source according to the flow shown in FIG.
2) Measurement of LED lamps
If the hazard information of the light source is known, the luminaire manufacturer can classify the luminaire according to the data provided in Fig. 1 according to the data provided by the luminaire. If the light source lamp mounted falls Ethr for RG2 category or a small light source, the system can also be used for measuring the minimum safety distance dmin.
If the source information is unknown, lighting manufacturers may use the system to measure the brightness of the lamp, and the spectral radiance of information, according to IEC 62471 or IEC / TR 62778 standard requirements blue lamp hazard classification. At this time, the conditions of the brightness measurement should be as consistent as possible with the actual application conditions, including the operating conditions of the luminaire, the test distance, the measurement field of view, etc., in order to effectively classify the luminaire.
3) System IEC 62471 standard test extension
The system is highly expandable, and can flexibly configure various measuring instruments, test a full set of photobiohazard parameters required by IEC 62471, and classify the tested light sources or lamps to meet the requirements of multiple measurement requirements, such as certification. Laboratory and a wide range of lighting manufacturers. In addition, the system can also IEC 62471 and IEC / TR 62778 compared to two standard tests to help manufacturers to identify the true level of hazard lamps depending on the application.
4 summary
The testing and evaluation of LED blue light hazards is imperative, and relevant international standards will be adopted or enforced in various regions of the world in the near future. China's current technology and equipment for measuring the blue light hazard of light sources and lamps have been developed. It is necessary for LED light sources and lamp manufacturers to pay attention to the measurement and evaluation of LED light sources and blue light hazards of lamps, and to make safety signs for the lighting application products of terminals. This is not only a necessary choice in response to the implementation of the standard, but also an effective means to further increase the market's confidence in the consumption of LED products.
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