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Apr 2, 2022 | Blog

Total Harmonic Distortion in LED lights

LED lights are one in all the foremost energy efficient lights used in most applications like indoor, outdoor, industry or even Landscape. But LED lights are equipped with non-linear inductive and capacitive loads which induce harmonics. Harmonics can cause interference on the electrical system and it can be detrimental in terms of both producers and consumers. Total harmonic distortion (THD) is defined as the sum of all harmonic components (refer Fig-1) existing electrical and electronic devices which is expressed in percentage.

Problems caused by Harmonics:
LED drivers are electronic power supplies in LED luminaires that contain non-linear (reactive and capacitive) elements. They modify the current signal which is being drawn from the supplied voltage signal and the signal becomes less sinusoidal. Most LED drivers also include rectifiers which convert the AC signal to DC. The switching operation of these rectifiers generate discontinuous currents which greatly distort the actual signal.

So when a LED driver is connected to an electrical system, it can generate harmonic currents that ultimately distort the supply voltage. With the more luminaire in an electric circuit, the distortion on the distribution system becomes more, which makes it inefficient and ultimately affecting the performance of other equipment.

Reduction of THD:
Passive filter is most commonly used as filtering techniques for mitigation of harmonics as it offers a low impedance path to divert the harmonic current caused by the non-linear loads. The passive filter consists of one inductor with one capacitor (refer Fig-2) to form an LC filter. This LC filter only passes low frequency and reduces high frequency.

We know that the 3rd harmonic is the predominant component of all the harmonics, so the filter is designed to eliminate the 3rd harmonics mostly along with the other harmonics.

THD limits as per international standards:
ANSI C82.11 states that the maximum THD of electronic ballasts should not exceed 32 percent. Electronic ballasts today are rated at less than 15 percent or even less than 10 percent THD. The magnetic ballast is rated in 20 to 28 percent range. Additionally EN 50160 and IEC 61000-3 states that the THD should be less than 10%.

Most Legero LED lights are having THD less than 10% conforming both EN 50160 & IEC 61000-3 standards which gives an optimized performance with maximum lifespan. To know more about us please visit or write to us at


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