1 Overview In recent years, the rapid development of LED research and development, production and application. The invention of Languang LED makes it possible to apply LED in general lighting field. With the continuous breakthrough of high-efficiency and high-power LED technology, LED will most likely become the most widely used illumination source in this century.
Both the Chinese government and the international community have paid great attention to the development of LED. The second division of the International Commission on Illumination (CIE), Division 2: Measurement of Light and Radiation, is dedicated to the measurement of LED characteristics and has been held twice by experts from the world's most famous and representative experts. The meeting has achieved certain results. However, the physical measurement problem of LED has not been solved in the south. In June this year, CIE held another CIELED Expert Seminar (CIELEDExpertSymposium) in Japan to further explore the characteristics measurement of LED.
For the characteristics of LEDs, because of the different application fields, there is a clear understanding of LEDs. The semiconductor industry and the lighting industry have obvious differences in LED understanding. They are used to indicate (including display) the characteristics of the target LEDs and the characteristics of the LEDs used for illumination purposes. There are also differences, the corresponding physical measurement methods and quality assessment methods are also different, and there are certain differences in the instruments used.
Whether it is a single packaged LED or an LED source consisting of LED strings, it is not the point light source or Lambertian source that is the most easily understood and described in physics. It is a discrete point composed of multiple equivalent point sources. A collection of light sources (like: both virtual and real images, mostly virtual). The specific point source set corresponding to the LED light source has the same characteristics: 2.1 the light intensity distribution is different at different distances of the near field; 2.2 near field illumination at a certain angle (such as normal) The intensity is not constant, therefore, the law of illumination is inversely proportional to the square of the distance; 2.3 Due to the positional sensitivity of the LED chip and the package lens and the asymmetry of the LED chip, the LED light source has different light intensity distribution curves on different C planes. 2.4 The "white light" LED, which has been industrially produced, has a spectral mixture that is not uniform. Its color distribution is like the light intensity distribution curve, which varies with distance and angle, especially pcLED, which often exists. A blue center with a high color temperature.
3 The measurement method and instrument for LED light source for general illumination is precisely because the above-mentioned characteristics exist for LED light source for general illumination, and the measurement and quality evaluation require specific methods and special equipment to solve. CIE has developed some standards for LED measurement, some standards are still being developed, and some standards will become the joint standard of CIE/ISO and CIE/IEC to unify international LED measurement problems. Although there are only a handful of science and technology workers in China engaged in LED measurement, China's LED measurement methods and instruments have been tracking the latest developments in the world and have received the attention of CIE. The following describes the physical measurement methods and instruments of the main characteristics of the illumination LEDs one by one: 3.1 The measurement of the average normal light intensity 127-1997 gives a clear specification and description, and clearly expresses the basic measurement method, which is a measurement instrument based on CIEPublication No. 127. In addition to the CIEConditionA and B, the instrument can also rotate the angle of the LED under test to measure the average light intensity of the LED at different angles.
3.2 Measurement of the average light intensity distribution curve and the absolute light intensity distribution curve In fact, as long as the LED in the middle is rotated at the 0 angle with the front vertex as the center, the illuminance value is recorded at different 0 angles, and then calculated according to the inverse square law of distance The average light intensity, then the obtained curve is the average light intensity distribution curve under CIEConditionA, B, respectively.
Although the above has stated that the LED does not conform to the characteristics of the point source and does not satisfy the inverse square law of distance, when the distance is sufficiently large, such as: ten times larger than the specific point source set (image) corresponding to the LED source, the distance is squared. The inverse law is restored to conformity. Since the angle formed by the detector aperture is small enough at this time, the word “average†is no longer important, and the word “absolute†can be added, but it can be omitted. It is the light intensity distribution curve of a 1W illumination LED under CIEConditionA and B respectively. It is the (absolute) light intensity distribution curve of this 1WLED at 1 meter, 3.16 meters and 10 meters respectively.
The (absolute) light intensity distribution curves of 1WLED at 1m, 3.16m and 10m respectively. It is important to note that when testing the average and absolute intensity distribution curves of LEDs, we must pay attention to the selection of the plane to be measured. For the sake of convenience, In this paper, the plane defined by the center of the LED is defined as the C0 plane, and the distribution of the light intensity with the 0 angle is measured on this plane. Testing at long distances (dot light source conditions) may involve a higher sensitivity wide linear dynamic range illuminometer, which is a relatively expensive instrument and requires a relatively high test environment. See related test instruments.
The requirement of 127, the detector is pressed, this creative technology has been applied for as a Chinese patent by a distant company.
The system diagram of the luminous flux and color measurement principle is measured by the Si-V (X) detector as required by the 84-1989. This method has a very good linear dynamic range for measuring the luminous flux. The spectral power distribution of the illuminated LED is measured by the spectroscopic method consisting of a monochromator and a PMT according to CIEPublication No. 63-1984, and then the Si-VU detector is automatically calibrated in real time using the SCF correction method described in GEPublication No. 127-1997. Measuring the luminous flux system. The correction factor is: Pan Jiangen. LED light, color and electrical parameters comprehensive performance analysis test principle and instrument
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