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Energy certification and labelling of buildings according to the Commission's Energy Performance of Buildings Directive concerns four main energy consuming systems with lighting as one of them. Previously there was neither practice nor experience with certification of lightings systems. First practical experience brought a series of questions and problems to be solved on methodological level. Main goal of the paper is to treatise on identified problems with evidence shown on practical case studies. Imperfections in the light of stressed necessity to run the certification process evolved a big amount of research works performed in order to improve the methodology and to investigate energy saving potential in buildings with new approaches. For each individual problem a solution is developed, which is now already implemented to the legislation on national level and put in practice. It is expected that these solutions may help to improve the current methodology by revision of the standard and this way to become a broader acceptance. Practical experience will help to support this effort. Solutions are introduced in this paper.In final part of the paper, a software tool developed for calculation of LENI is presented. Important feature of the software named EHB LiteCalc is that all steps of calculation can be separately inspected, also giving the user possibility to enter the calculation process by inputting manually forced values. This special option can serve for experimental purposes.