The quality of energy is great importance as much as the electricity is required in power systems. One of the most important factors affecting the power quality is the harmonics resulting from non-linear loads in the system. In recent years, the development of the power electronics causes non-linear loads to increase. Correspondingly, it causes waveform distortions and harmonics in power systems. Harmonics cause technical and economical losses in the system. Except for some precaution to take in the design phase of a power system, the most important method for reducing harmonics is the use of harmonic filters. In this study, harmonic measurements of fluorescent lamp with electronic ballast are taken. Thereafter, passive filters are designed to reduce harmonics, their effects and decreases in Total Harmonics Distortion (THD) values are observed. Single-tuned and double-tuned models are used in filter design. The same system is modeled in Matlab/Simulink, the theoretical results are compared with measurement results.