A very important parameter in the illumination – the power factor (PFC) is often easily overlooked, so what’s the power factor, what’s the useful of the power factor?

1.Power factor

The power factor characterizes the ability of the illumination to output active power. Power is a measure of the transmission rate of energy, which is the product of voltage V and current A in a DC circuit. In an AC system, it is more complicated: some AC currents do not transmit power in the load. It is called reactive current or harmonic current, which makes the apparent power (voltage Volt multiplied by Amps) greater than the actual power. The unequal power and actual power lead to a power factor, which is equal to the ratio of actual power to apparent power. So the actual power in the AC system is equal to the apparent power multiplied by the power factor. Namely: power factor = actual power / apparent power. Only the power factor of linear loads such as electric heaters and bulbs is 1. The difference between the actual power and the apparent power of many devices is small and negligible, while the difference between capacitive devices such as lamps is large. Very important. A recent study by PC Magazine in the United States showed that the typical power factor of a illumination is 0.65, which means that the apparent power (VA) is 50% larger than the actual power (Watts)!

2.Inspecting power

Apparent power: the product of the AC voltage and the AC current. Expressed as: S = UI. Where, S is the rated output power, the unit is VA (volt-amperes); U is the rated output voltage, the unit is V, such as 220V, 380V, etc.; I is the rated output current, the unit is A. Apparent power consists of two parts: active power (P) and reactive power (Q). Active power refers to the part that works directly. For example, the lamp is turned on, the motor is rotated, and the electronic circuit is operated. Because this power becomes heat after work, it can be directly felt by people, so some people have an illusion that the active power is regarded as apparent power. I don’t know that the active power is only a part of the apparent power. :P=Scosθ=UIcosθ=UI•F. Where P is the active power in W (Watts); F = cos θ is called the power factor, and θ is the phase difference when the voltage and current are out of phase with each other in the non-linear load. Reactive power is the portion of power stored in the circuit but not directly working, expressed as: Q = Ssin θ = UIsin θ. In the formula, Q is reactive power and the unit is var.

For illumination and all other electronic circuits that operate on DC voltage, leaving reactive power is simply not working. The average user believes that devices such as lamps only need active power and do not require reactive power. Since reactive power does not work, what is it to use! So of course they think that the lamp with a power factor of 1 is the best. Because it gives the maximum output power. However, this is not the truth.

If there is a kind of lamp, when the AC mains input is rectified, the pulsating DC voltage is obtained. If the pulsating voltage is not processed, it is directly supplied to the lamp. There is no doubt that the circuit cannot work normally. Although the power factor of the illumination is close to 1, then what is the use? In order for the illumination circuit to function properly, it must be supplied with a smoothed DC voltage. This “smoothing” operation must be done by a filter capacitor C connected to the rear of the lamp rectifier. This filter acts like a reservoir. The capacitor must store a sufficient amount of charge. When rectifying the gap between the half waves, the operating voltage on the circuit is still uninterrupted and can maintain a normal level. In other words, even if there is no input energy between the two pulsating half-waves, there is no significant change in the voltage level of Uc. This function is realized by the energy storage in the capacitor, and this part of the energy stored in the capacitor. It is reactive power. Therefore, the illumination is supported by reactive power to ensure that the circuit correctly uses the active power for normal use. Therefore, it can be said that the illumination not only needs active power but also reactive power, both of which are indispensable.

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