| The color temperature indicates how much the light emitted by the light source contains color components,it can evaluate the quality of the light source.In real life,the chromaticity coordinates of most light sources do not lie exactly on the blackbody locus,so the concept of color temperature is extended to correlated color temperature(CCT).Therefore,the calculation method of CCT is very important and has been a research hotspot.At present,the calculation methods are mainly divided into tow categories: the iterative method and the look-up table method.The iterative method can calculate a wide range of color temperature,but highly dependent on the initial value.The look-up table method is simple and more popular in practical applications,but it highly depends on the look-up table.Both types of the methods have unavoidable drawbacks,so the thesis maked a deep research on the two kinds of methods and propose new methods.Firstly,it found that some light sources generated by LED spectral optimization deviated from the blackbody locus far beyond the range specified by the International Commission on Illumination(CIE),and the distance function between the light source and the blackbody locus has a local maximum point,which leads to all methods are not applicable.In order to solve these problems,three innovations have been proposed.First,the concepts of generalized correlated color temperature(GCCT)and generalized color deviation(GDuv)are proposed to describe the light source points beyond the range specified by CIE.Second,descending Newton iterative method is proposed,which can still converge to the local minimum point rather than the local maximum point in the process of LED spectrum optimization.Third,the CIE 1960 UCS chromaticity diagram is divided into six regions according to the characteristics of the distance function between the light source points and the blackbody locus,then a hybrid iterative method based on Newton iterative method and descending Newton iterative method is proposed.Secondly,Ohno proposes a hybrid method based on triangular method and parabolic method to calculate the CCT and color deviation(Duv).The test results show that there is still improvement in using the parabolic method to calculate the distance between the light source point and the blackbody locus.So this thesis proposes two new hybrid methods,when |Duv|<0.002 the triangular solution is used,and when |Duv|≥0.002 the parabolic method be replaced by the spline interpolation method or the third order interpolation method with two local function.Finally,a large number of tests are carried out on the proposed method.The test set is built by simulation strictly according to the definition of CCT and Duv.The test results show that the calculation error of the hybrid iterative method is lower than0.002 K,which can be used in the process of LED spectrum optimization.The thesis also uses two kinds of look-up tables to test the two improved methods of Ohno method.The results of the two improved methods are close and the errors are obviously smaller than that of Ohno method.And the two improved methods can reduce the maximum calculation error from 1.2484 K of Ohno method to 0.3858 K by only using 1% look-up table.The hybrid iterative method proposed in this thesis has important application value in LED spectrum optimization.At the same time,the research content of this thesis has important reference value for CIE to establish unified computing standard. |
