The significance of the power factor for LED luminaires

The power factor is an important parameter of LED fixtures, let's learn more about what is the power factor below.

1. Power factor

The power factor characterizes the ability of a luminaire to output active power. Power is a measure of the transmission rate of energy, and in a DC circuit it is the product of voltage V and current A. In the AC system, it is more complicated: that is, part of the AC current cycles in the load and does not transmit electrical energy, which is called reactance current or harmonic current, which makes the apparent power (voltage Volt times current Amps) greater than the actual power. The power factor is equal to the ratio of actual power to apparent power. Therefore, the actual power in the AC system is equal to the apparent power multiplied by the power factor. That is: power factor = actual power / apparent power. Only linear loads such as electric heaters and light bulbs have a power factor of 1, and the difference between the actual power and the apparent power of many devices is small and negligible, while the difference between capacitive devices and lamps is large and important.

2. Apparent power

Apparent power: i.e., the product of the AC voltage and the AC current. It is expressed by the formula: S=UI. where S is the rated output power, and the unit is VA (volt-ampere); U is the rated output voltage, the unit is V, such as 220V, 380V, etc.; I is the rated output current in A. The apparent power consists of two parts: active power (P) and reactive power (Q). Active power refers to the part that does the work directly. For example, to make the light shine, to make the motor turn, to make the electronic circuit work, etc. Because this power becomes heat after doing work, it can be directly felt by people, so some people have an illusion, that is, they regard the active power as the apparent power, but they don't know that the active power is only a part of the apparent power, which is expressed by the formula: P=Scosθ=UIcosθ=UI? F。 where P is the active power in W (watts); F=cosθ is called the power factor, and θ is the phase difference when the voltage and current are not in the same phase at a nonlinear load. Reactive power is the part of power that is stored in the circuit but does not do work directly, and is expressed by the formula: Q=Ssinθ=UIsinθ. where Q is the reactive power, and the unit is var.

3. Reactive power

For lamps and all other electronic circuits that work on DC voltage, they cannot work without reactive power. The general perception is that devices such as lamps only require active power and do not need reactive power. Since the reactive power does not do work, what is the use of it! So, of course, they think that a lamp with a power factor of 1 is better. Because it can give a large output power. However, this is not the case.