Improve the accuracy of LED flux measurement in integrating sphere

Improve the accuracy of LED flux measurement in integrating sphere

  • 2020-12-07
  • Views:0

Improve the accuracy of LED flux measurement in integrating sphere

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  • Categories:NEWS
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  • 2020-12-07
  • Views:0

Different from the traditional light source, the flux measurement of LED light source in the process of using integrating sphere to measure the luminous flux poses great challenge to the accuracy of the equipment. On the one hand, compared with traditional light sources, leds are generally more directional and do not emit light uniformly throughout the space. This feature makes the direct light distribution of LED on the surface of the integrating sphere uneven. This uneven distribution will result in different LED direct light with different detector reflection characteristics. Since the position of detector and baffle are fixed, the direct performance of various reflection distributions is signal fluctuation. In the common test system, leds with different lighting angles are different, and the same LED is placed in different directions and has the same emission at different positions. Even if the rated luminous flux is the same; The actual measurements are different. According to the customer's verification results, the influence of the LED placement direction of the ordinary LED testing system on the luminous flux measurement results is always more than 50%(the difference between the maximum and minimum signals of the same LED measured in different directions).

The internal reflection characteristic of integrating sphere is one of the key factors that make LED directivity affect measurement accuracy. In ordinary LED testing system, the reflectivity and Lamber properties of the coating on the integrating sphere surface are not ideal. One reason is low reflectivity and the other is poor diffuse reflectance. The result of the low reflectivity of the integrating sphere surface is that the direct light of the LED gradually decays after several reflections. However, in the whole process of light mixing, direct light and reflected light occupy a large proportion, which is dominant. In some cases, low reflectivity materials can have a strong shadow effect on the back of the baffle probe. However, this is the linear reflection of the shadow effect resulting in inaccurate measurement.
In addition, the lower diffuse reflection rate will seriously affect the attenuation of the signal. In the course of light measurement, the light is reflected in the integral sphere for many times, each reflection will produce a certain attenuation, but the influence of the reflection degree on the light intensity will be strengthened after many times of reflection. For example, the reflected light is reflected 15 times in the integral sphere, and if there is a 5% difference between the reflectivity, the signal attenuation may be more than doubled. In fact, the difference in reflectivity of the integrating sphere is much greater than that.
The current LED test system is not yet used as a standard LED as a standard light source. The standard halogen tungsten lamp was selected as the standard light source during the measurement. Due to the large difference in the external structure of standard light and measurement LED, including the influence of LED lamp holder's light absorption and the difference between standard light installation position and LED installation position, all of these are important factors affecting the accuracy of test results.



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