Power Factor Correction Techniques in LED Lighting

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High power LED based light fixtures are replacing fluorescent and HID light sources in many general lighting applications. Since LED lighting represents a green technology, the issue of power factor is very important. Power factor is defined as the ratio of real power consumed by a load (expressed in Watts) to apparent power (expressed in VA), which produces a figure from zero to unity that indicates the degree of distortion and phase shift in the current waveform. The overall power factor is the product of the distortion power factor and the displacement power factor, where displacement power factor considers only the fundamental of the current and distortion factors in the harmonics.

Real power is defined as the apparent power multiplied by the power factor, where the apparent power is the product of (rms) voltage and current. This relationship indicates that more current is required to provide the same amount of real power for lower power factors.

Low power factors negatively impact the environment because transmission lines lose more power in the form of heat proportional to the square of the current. Higher current results in wasted energy in transmission lines as well as generators and transformers consuming more fossil fuels and generating more pollution and higher costs. Clearly, high power factor is very beneficial in all electrical products that operate from the AC power grid!

Although individual lights consume relatively small quantities of power (typically 10 W to 100 W), lighting is nevertheless very significant since somewhere around 20 percent of the worlds electricity produced is consumed for this purpose.

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