1 Overview The rapid development of LED research and de […]
1 Overview The rapid development of LED research and development, production and application in recent years. The invention of Languang LED makes it possible for LEDs to be used in the field of general lighting. With continuous breakthroughs in high-efficiency and high-power LED technology, LEDs will likely become a widely used lighting source in this century.
Regarding the characteristics of LEDs, due to the different application areas, a unified understanding is needed. There are obvious differences in the understanding of LEDs between the semiconductor industry and the lighting industry. The characteristics of LEDs used for indication (including display) purposes and the characteristics of LEDs used for lighting purposes There are also differences, the corresponding physical measurement methods and quality assessment methods are also different, and the instruments used are also different.
Whether it is a single packaged LED or an LED light source composed of LED strings, it is not a point light source or Lambertian light source that is easy to understand and describe in physics. It is a scattered point composed of multiple equivalent point light sources. A collection of light sources (image: both virtual and real images exist, and most of them are virtual images). The specific point light source set corresponding to the LED light source has common characteristics: 2.1 at different distances in the near field, its light intensity distribution is not the same; 2.2 at a specific angle (such as normal), its near field emits light The intensity is not constant, therefore, the law of illuminance is inversely proportional to the square of the distance does not hold; 2.3 Due to the position 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 At present, the "white light" LED that has entered industrial production has uneven spectral mixing, and its color distribution is like a light intensity distribution curve, which changes with distance and angle, especially pcLED, which often exists A blue center with a high color temperature.
3 Measurement methods and instruments for LED light sources for general lighting. Because of the above-mentioned characteristics of LED light sources for general lighting, specific methods and special equipment and instruments are needed for measurement and quality evaluation. CIE has formulated some standards for LED measurement, and some standards are still under development. Some standards will become joint standards of CIE/ISO and CIE/IEC to unify international LED measurement issues. Although there are only a few scientific and technological workers in China who are engaged in LED measurement, China's LED measurement methods and instruments have been tracking the world's *new developments, and have received the attention of CIE. The rotation angle of the tested LED can be used to measure the average light intensity of the LED at different angles.