After the emergence of LED lighting, the measurement problem has been a hot topic. This paper combines the research, practice and analysis of luminosity, colorimetric measurement and measurement equipment knowledge with the research on the accuracy and consistency of light color measurement of LED lighting products funded by the Guangdong Provincial Bureau of Quality and Technical Supervision. Some questions put forward their own views and opinions to share with you.
I. Overview of photoelectric conversion devices and instruments for light color measurement
Illumination optical measurements are generally divided into two measures of luminosity and chromaticity. At present, in the measuring device system for illumination light color parameters, there are relative method measurement (such as integrating sphere photochromic measurement system, etc.) and absolute method measurement (such as photometric and chromaticity distribution meter measurement system, illuminance meter, luminance meter, etc.) Big class.
Most of the illuminance meters used in lighting engineering measurement, the majority of the brightness meter still use the integral method photometric probe; the integrating sphere measurement system for the light color parameter measurement of the illumination product has basically not used the integral method photometric probe and uses the spectroscopic spectrometer, first The spectral power distribution is measured, and the total luminosity parameter and the total chromaticity parameter are calculated by the software; the illuminance probe is still used in the illumination product light color distribution meter measurement system, and the luminosity parameters in all directions are measured and recorded, and the software can be Calculate the total photometric parameter.
In addition, most light distribution meter systems are equipped with a spectral monochromator, including mechanical scanning, which measures the spectral power distribution in a certain direction by wavelength scanning. In principle, the measurement accuracy is high, but the speed is too slow; or CCD type The spectral power distribution in a certain direction is measured at one time, and the current precision is high and the speed is fast; or the tristimulus value instrument (one-time measurement of the three primary colors of red, green and blue in a certain direction, the fastest, but the precision is poor) It has basically not met the laboratory measurement accuracy requirements to measure the chromaticity parameters in all directions, and the total chromaticity parameters can be calculated by software at the same time.
Regardless of the relative or absolute measurement, the instrument must be calibrated or calibrated before leaving the factory, before use or after a period of use, and long-term history has formed a standard source of calibration using standard incandescent lamps. This has many advantages, but there are also some shortcomings. Whether using an integration method (photometric probe) or a measuring instrument using a spectroscopic method (spectrometer), the matching error coefficient f1' of the human eye spectral luminous efficiency function V(λ) (referred to as "visible function") is the illumination color The most important precision parameter in the measuring instrument, the smaller the f1', the higher the accuracy.
At present, various lighting inspection agencies and lighting enterprises have a large number of integrating sphere spectral light color electrical measurement systems and a number of light color distribution meter measurement systems, and a large number of illuminance meters. There are domestically produced, also imported, there are early purchases (generally f1' larger), but also recently purchased (generally f1' is smaller). As the majority of device users, it is generally only known what the nominal photometric probe index f1' of the device is, and it is not clear what the actual f1' is. I don't know which wavelengths and bands of red, green, and blue wavelengths are different. These make it possible to produce large errors when measuring lighting products that differ greatly from the spectral distribution of standard incandescent lamps. And it is not known which measurement bands are mainly from which bands.
It has been reported [1] that even with the most accurate photometric probe (f1' = 0.5%) of the matching function error coefficient f1's currently seen, the error for the blue band measurement is very impressive, see Figure 1.
Of course, the latter analysis will mention that the measurement error of the blue band has less influence on the total luminous flux error of the entire visible light band, but the influence on the chromaticity error will be large.
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