In the field of electrical engineering, the power factor φ expresses the ratio of real power P to apparent power S (see formula):
λ = P / S
Real power P is a physical value that constitutes the amount of transferred power. Apparent power S is a product of effective voltage and effective current, and thus more of an "artificial" concept that serves to specify the loads acting on means of transfer (e.g. conductors). As a result, the power factor λ is always positive and ≤ 1. It defines the degree to which power is converted into usable energy in a device.
In accordance with the IEC 62384 performance standard, the power factor for LED drivers is displayed on the type label as follows:
λ = 0.95
The efficiency of a device is defined using its power efficiency factor η. The power efficiency factor of a device is defined as the output power Pout divided by the input power Pin. The measuring procedure for LED drivers is defined in the IEC 62442-3 standard, which is currently under preparation. High-quality devices feature a power efficiency factor greater than 85% (η ≥ 0.85).