ensures that the sensitive nearby electrical/electronic equipmentor lamp will be not affected by the generated harmonics. Table 5shows the limited harmonic current of lighting equipment accord-ing to the mentioned standard.For an electronic ballast of brand B, the harmonic measurementis also performed by the power spectrum analyzer, and the resultis shown in Fig. 10. To evaluate the harmonics obtained and illus-trated in Fig. 10, each order of harmonic current from 4 lamps and10 lamps is considered and compared with the IEC standard. Atthe first order (fundamental frequency), since it is used as refer-ence for other harmonic orders, it is found that for the obtainedharmonic currents of 4 lamps and 10 lamps, they have the samevalue (100%f). In addition, for the second order, it can be seen thatthe obtained harmonic current of both case has a value less thanthe IEC standard level. Generally, in any electrical systems, the oddorder of harmonic current is mostly occurred in comparison withthe even order, therefore, the harmonic current of even order hasmuch less value. Based on a further analysis of Fig. 10, by consider-ing the odd order, it can be observed that the harmonic current of 4lamps is less than that of the 10 lamps and more than the IEC stan-dard, except for the third order and fifth order. As a result, whencomparing the result with the standard, some orders exceed themaximum harmonic current permitted, so a passive harmonic fil-ter will be designed and added at the input of the T5 fluorescentlamp connecting to the electronic ballast.This filter is simply composed of one series inductor and oneparallel capacitor. The resistor of the order of M can be added inparallel with the capacitor to discharge its electric charge and alsofor mechanical structure. The mentioned structure corresponds toa low-pass filter that the advantages are: (1) it does not allow highorder harmonics that the frequencies are superior to the chosencut-off frequency to pass through electrical source, (2) it is easy tobe implemented, (3) it uses few components to function, and etc.To reduce the harmonics magnitude, the cut-off frequency isa key parameter to be considered. Here, the cut-off frequency of