This diploma thesis presents the efficiency of various light sources which are used for lighting on a daily basis (incandescent light bulb, halogen lamp, compact fluorescent lamp, light-emiting diode). The theoretical part of the thesis presents the instruments used for measurements, the physical laws used in order to calculate the efficiency of each light source and the physical background needed for the understanding of further calculations. The experimental part of the thesis presents the spectrometer calibration using an incandescent light bulb, which radiates as a black body, therefore Planck law can be used for the calibration. Using the calibrated spectrometer, the spectrum of various light sources were acquired and the efficiency of the light sources in the visible part of the spectrum were calculated. In the conclusion of the thesis, efficiency of different sources is compared.