More about Power Factor

What is Power Factor?

Active power is the amount of power supplied by the utility that can be translated into useful work and is typically defined in terms of Watts. Reactive power is the electric power that is consumed by a mechanism such as a lamp but does not actually produce any form of useful work and is typically defined as Volt Amps. The sum of active and reactive power is the sum total of power actually supplied by an electric utility to run an electronic device.

The ratio of active power or real power measured in Watts to total power measured in volt-amperes is called Power Factor (PF). Power factor is characteristic of alternating current (AC) circuits and is always expressed as a number between 0 and 1 or 0% and 100% with 1 or 100% being a perfect Power Factor. When a device has a Power Factor of less than 1 or 100%, the device consumes electricity but only part of this energy is actually used to power the product.

Incandescent bulbs have a perfect Power Factor of 1.0, but many of the brand name CFL bulbs on the market have Power Factor ratings of .7 or lower.

Power factor is a matter of significance for power generating utilities because it measures how much power is actually generated compared to the amount of power consumed by customers. Utility companies supply customers with volt-amps but bill them for Watts consumed, and Power Factors below 1.0 require a utility to generate more than the minimum energy necessary to supply the needed power. This situation increases generation and transmission costs. In fact, in commercial settings utilities may impose Power Factor correction penalties on customers who do not have high overall Power Factor ratings. Unless high Power Factor CFL bulbs become the norm for residential usage, industry experts expect utility companies to impose a similar penalty for Power Factor correction in the residential market in the near future.

Regulatory and standardization agencies recognize that energy efficient lighting and a lighting system’s electronic ballast interface contribute to an end-user’s overall power factor. Limits have been established for acceptable product Power Factors. For instance, the American National Standards Institute (ANSI) recommends that all commercial indoor, hard wired ballasts meet a minimum power factor of 0.9 and requires residential hard wired luminaires below 120 Watts to
meet a minimum Power Factor of .5. While the standards currently reflect a low density of products, the concern within the utilities industry is that standard setting organizations are not considering the overall Power Factor impact of replacing hundreds of millions of incandescent bulbs with CFL bulbs of varying Power Factor ratings.

Power Factor Comparison Study

The table below illustrates a comparison between a traditional 75 Watt incandescent bulb and three types of energy efficient CFL bulbs. The VA savings achieved with the CFL bulbs relative to the traditional incandescent light is clearly significant in all cases and ranges from approximately 40% in the normal power factor (NPF) case up to approximately 70% in the high power factor (HPF) case. Among the CFLs, while the level of real Watts consumed is practically identical in each of these energy efficient
products independent of their respective level of power factor correction, their actual level of VA power consumption begins to differ meaningfully when power factor levels are taken into consideration.

Energy Requirements for a 1200 Lumen Screw In Lamp