Ms. Lin Jiang Profile

Lin Jiang

at National Inst of Metrology

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Proceedings Article | 18 November 2019 Paper

Uncertainty evaluation of colour correction factor using Monte Carlo method in LED photometry measurement

Weiqiang Zhao, Hui Liu, Jinyun Yan, Ying Su, Lin Jiang

Proceedings Volume 11189, 111891V (2019) https://doi.org/10.1117/12.2538759

KEYWORDS: Light emitting diodes, Photometry, Monte Carlo methods, LED lighting, Light sources and illumination, LED displays, Luminous efficiency, Metrology, Numerical simulations, Mathematical modeling

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Nowadays, Light Emitting Diode (LED) and related products are popular in everyday lighting. Especially colour LEDs are widely used in colour application such as outdoor display, traffic signal light and cars. Precise photometric measurement results for those LED products are necessary due to needs of the international or domestic commercial trade. In the testing lab, people usually use photometer and related photometry equipment to measure LEDs. The photometer mimics the human eyes however it is not exactly the same. Thus, colour correction factor (CCF) is applied when the relative spectral response of the photometer S*(λ) is different from the photopic luminous efficiency function V(λ). Since the CCF is the most significant uncertainty component in LED total luminous flux and averaged LED luminous intensity measurement, the evaluation of uncertainty of CCF become more important in National Institute of Metrology China (NIM). Recently the Monte-Carlo method, as known as numerical simulation technique, is utilized to evaluate uncertainty by generating millions of random variable with related distribution function. The input mathematical model of the photometer S*(λ) and spectra of measurand PLED(λ) are described. The propagation of the uncertainty is also introduced. Examples of the evaluation of CCF uncertainty are shown.

Proceedings Article | 2 November 2018 Paper

A timeline-based sampling method applied in National Institute of Metrology primary standard goniophotometer

Weiqiang Zhao, Hui Liu, Jingyun Yan, Ying Su, Lin Jiang

Proceedings Volume 10819, 1081918 (2018) https://doi.org/10.1117/12.2325366

KEYWORDS: Goniophotometry, Light sources, Metrology, Standards development, Signal processing, Lamps, Light emitting diodes, Photodetectors, Visible radiation

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The SI derived unit lumen is a unit of total luminous flux, describing a total quantity of visible light emitted from a light source. The realization of lumen unit is implemented by the facility called goniophotometer in National Institute of Metrology China (NIM). The goniophotometer is a facility measuring the luminous intensity of a light source at various angles, and the total luminous flux is calculated by integrating the spatial distribution of luminous intensity. Because of sampling characteristic of the goniophotometer, the spatial distribution of luminous intensity is a discrete curve. In our previous method, the goniophotometer measure the luminous intensity value at polar angle step size of 1°, 2° or 5°. For measurement of LED-light sources, which are likely oriented light sources, the spatial distribution of light is not homogeneous. Carefulness must be taken because the choice of angle sampling interval is going to be a considerable uncertainty component. Recently, a timeline-based sampling method is developed and applied in the primary standard goniophotometer in NIM, to realize the lumen unit, as well as measuring the LED light sources. The control computer is not to record the luminous intensity at exact integer angle, but to record the luminous intensity and its related time, and to record the angle and its related time. These two record threads are running respectively and simultaneously during the whole testing process. An interpolation is used to calculate out the luminous intensity and the angle at the same timeline. Thus, the spatial distribution of luminous intensity curve has much more effective data than that from the previous method. It is an improvement to help to get a more accurate result. The repetitive fluctuation is evaluated to be 0.025%, a much lower level than that of the previous method.

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