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 is based on IEC 62471 and simplifies the measurement of the blue light hazard of light sources and luminaires. 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.
2.2 LED blue light hazard classification
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.
Among them, "Ethr for RG2" is suitable for the case where the blue light hazard-weighted radiance may exceed the RG1 limit or the irradiance is unmeasurable. Ethr is the illuminance value of the RG1 and RG2 boundary, which is used to determine the hazard limit distance dmin. 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.