Under the artificial sky was measured the light transmission efficiency of direct hollow light guide. Firstly, only tube with diameter of 530mm and length of 1170mm was investigated. Secondly a sample with additional diffuser, thirdly a sample with cupola and fourthly a sample with cupola and diffuser were tested. Simultaneously analytic methods for calculation of the light transmission efficiency were applied to test theoretical results with experimental. There were used three calculation methods - Luxplot Package model, approximate sizing method according to document CIE 173:2012 and HOLIGILM - software for prediction of indoor illuminance. The paper discusses results of experimental measurements and results obtained from calculations. It was found that difference between measured values of light transmission efficiency and calculated values were up to 3% according to CIE method and programme HOLIGILM and circa 8% according to Luxplot Package model.