Power Factor Correction (PFC) is increasingly important because it contributes significantly to energy efficiency. Power factor values lie between 0 and 1; the higher the value, the better the efficiency. A purely resistive load has a ‘perfect’ power factor of 1, meaning that it takes only active power from its power source, all of which is used. However, most electrical and electronic equipment, including power supplies, takes extra power which isn’t consumed. Instead this power goes into the electromagnetic fields of transformers, motors and other inductive devices, as well as into charging capacitors. Although this reactive power is not dissipated or useful, it still has to be generated by the power source, and this leads to energy inefficiency. Therefore, the more a device’s power factor can be improved, the lower its reactive power input and the higher its efficiency.


If a power supply takes 240V at 1A with a power factor of 0.5, its active power consumption is 240 x 1 x 0.5 = 120W
If the same power supply has an improved power factor of 0.9, its active power consumption becomes 240 x1 x 0.9 = 216W – an improvement of 96W, or 80%!
This is why Sunpower offers power supplies with Active Power factor Correction (APFC) giving a power factor of 0.9 or better. Using these will significantly reduce the mains loading and improve the energy efficiency of a LED lighting installation of any significant size. To maximise these supplies’ APFC capability, it is important to size them so that they are loaded to 75% or more of their rating.