WHAT IS POWER FACTOR AND WHY IS IT IMPORTANT?

Power Factor (PF) is a ratio used for AC supplied equipment that defines how efficiently the electrical power is being used in that system. It is a unitless number, typically represented as either a percentage or decimal. The closer to 1 or 100%, the more efficient the system is. The system could be as large as a home and all the AC equipment within it or an individual LED downlight with an integrated AC driver (see Figure 16 below).

Figure 16: Power Factor System

To help illustrate power factor, let’s look at an example. If a home had 10 downlights that draws 100W to operate (working power), but the utility company had to supply 125W of power to run the lights (apparent power), the Power Factor would be 80% or 0.80 (PF = 100W / 125W = 0.8). Hence, only 80% of the power supplied does any useful work.

In this example, the consumer is only paying for 100W of power, however, the utility company needs to deliver 125W of power. As we know, nothing is free. The utility companies do not absorb these added costs – they are factored in the electric rates. So, it would benefit all of us if all systems had a higher PF.

A Class 2 DC Distributive Lighting System is extremely efficient and will provide you with a power factor of greater than 0.9 or 90%. Energy Star only requires power factors of greater than or equal to 0.5 or 50% for fixtures that are less than or equal to 5 watts. If the fixture is greater than 5 watts, the requirement is 0.7 or 70% (Energy Star Program Requirements for Luminaires V2.2). Hence, the power factor for a Low Voltage, Class 2 system can be up to 40% greater than and more efficient than a traditional LED light fixture.