Measurement Uncertainty Of White LED Light Lumens

With the photometric measurement uncertainty of LED lamps being more and more important in interlaboratory comparisons,how to properly assess the uncertainty has become a major problem.Generally speaking,sources of uncertainty is directly related to people’s understanding about uncertainty knowledge,test principle, samples, equipment,testing methods and operation;some potential influential factors are difficult to determine;imperfect measurement model and strong correlation make it difficult to combine the uncertainties;maximum error limit and probability distributions of class B uncertainty is difficult to determine.Therefore,this thesis is aimed at exploring reasonable evaluation of lumens measurement uncertainty about white LED lights,including the sources of uncertainty,mathematical model and evaluation methods.First of all,through the literature research and testing practices,to collect uncertainty sources as much as possible.According to the evaluation ability,this thesis mainly considers18uncertainty sources.As a result,there is only8major uncertainty factors,while the contribution of other factors can be ignored.Second,establish a reasonable mathematical model of lumens.According to the testing principle,the established mathematical model contains only the spectral response of the standard lamp and LED lamp.For the other factors not included in the model,determine their impact respectively.Finally,combine uncertainty components together. As a result, this kind of model is very convenient for the determination of the uncertainty.Then, in the process of evaluation,the error of spectral energy and wavelength and the strong correlation between adjacent wavelengths increase the difficulty of evaluation. In this paper,first use cubic spline interpolation method to obtain spectra of integer wavelength points, then use ISO 《Guide to The Expression of Uncertainty》(short for GUM) and monte carlo method (MCM) respectively to determine uncertainty component introduced by the spectral energy error.At the same time,the spectral response of the LED lights will consider the influence of the wavelength error.All the calculations of GUM and MCM is conducted by Matlab.It was found that,for the nonlinear mathematical model of luminous flux,the result of MCM is smaller than that of GUM and MCM is more simple and accurate than MCM.For other factors not included in the model,use GUM,including designing experiments for class A component of uncertainty and get error distribution range for class B uncertainty through certificates, literature or experience. At last,through the uncertainty budget,there several major uncertainty contributions,including calibration uncertainty of standard lamp,spectral response of LED lamp,correction of light distribution mismatch,wavelength error,ambient temperature and DC current of standard lamp,nonlinearity and accuracy of Spectrometer.They can be controlled properly in the future measurement to minimize the measurement uncertainty...