How to design better, more efficient lighting systems

April 04, 2016 // By Mehdi Samii
A parallel capacitor is added across the inductive load
Mehdi Samii of Ametherm Inc. considers ways to design better, more efficient lighting systems.

There’s more than one way to build a lighting system, and good design leads directly to better power efficiency and a lower bill of materials cost.  Currently, the lighting industry is transitioning from 240 V to 277 V for greater efficiency.  This makes it an excellent time to introduce Power Factor Correction (PFC) to existing product lines.  As these systems need to be updated anyway, OEMs can take advantage of the many benefits of PFC at the same time.

The need for PFC arises from the move to inductive loads.  Traditional lighting applications used resistive loads such as incandescent lights.  However, resistive loads have the disadvantage that the resistance they introduce to the system generates heat.  This heat represents power losses and decreases efficiency.  To eliminate these losses, the lighting industry continues to move to inductive loads such as florescent lights that offer greater efficiency.  Figure 1 shows a lighting system based on an inductive load.

Figure 1: A parallel capacitor is added across the inductive load

Power Factor Correction

The unfortunate truth is that many OEMs implement inductive loads in a manner that severely curtails their efficiency.  In many cases, they are simply unaware that these issues can be easily and inexpensively resolved with Power Factor Correction.

By its nature, an inductive load shifts the voltage and current out of phase to each other.  Specifically, the inductive reactance introduced is out of phase with the system’s resistance.  This phase difference reduces the efficiency of the system.

The Power Factor (PF) is the ratio of the real power of the system to its apparent power, where apparent power is what you expect from the system and real power is what you actually get.  Depending upon the application, an out of phase system can drop to as low as 60% efficiency.

The goal of Power Factor Correction is to minimize the phase difference between voltage and current.  Capacitive reactance can be

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