Power Factor in LED Drivers: Why 0.9 Is Not the Whole Story

Animated · captions

NLC Academy · Episode 4

Power factor

The watt you pay for vs. the watt that lights the room.

The power triangle

Real power does the work. Reactive power is exchanged with electric and magnetic fields, with no net energy transfer over a cycle. Apparent power is RMS voltage times RMS current.

The definition

PF= Real powerApparent power =cos φ

A PF of 0.95 means that 100 kVA of apparent power delivers 95 kW of real power. It does not mean that the remaining 5% is an electrical loss.

On the driver datasheet

LED Driver · ElectricalDatasheet

Input voltage220-240 V AC

Output power100 W

Power factor Solar EV Charger Transformer LED Savings CCTV> 0.9

THD_i< 15%

State the threshold as a project target: true PF ≥ 0.90. Then verify it on site under the specified operating conditions.

Why it lands on the bill

More apparent power required

105 VA0.95

111 VA0.90

118 VA0.85

143 VA0.70

200 VA0.50

Power factor →Apparent power per 100 W of real power

For customers subject to Saudi Arabia’s power-factor tariff, PF below 0.95 carries an additional charge of 5 halalas per excess kvarh. Applicability depends on the customer category and tariff conditions.

The phase angle

Power factor is the cosine of the lag between voltage and current

What each part does

The coil makes current lag, the capacitor makes it lead

Coil first, then the capacitor

Perfect sine → a coil pushes current to lag → a capacitor bank's leading current cancels the lag and pulls φ back to almost zero

What the meter sees

The power triangle, and what sets conductor loading

The LED-driver twist

In phase, and still distorted

The fix

Active PFC: a boost inductor reshapes the current

The one rule

Demand > 0.9.
Verify on site.

NLC Power & Control Systems

0:00 / 0:00

Animated explainer, press play to watch the concepts now; the filmed cut publishes once production wraps.

How it works

Where the 0.9 actually comes from

Six diagrams for the cause the spec sheet hides: why current drifts out of step with voltage, how a coil drops the power factor and a capacitor bank claws it back, and why an LED driver still needs active correction to hold the number.

The phase angle

Power factor is the cosine of the lag between voltage and current

A pure resistor draws current perfectly in step with voltage. Anything reactive shifts the current by an angle φ, and the power factor is simply cosφ: 0° gives 1.0, more lag gives less.

What each part does

The coil makes current lag, the capacitor makes it lead

They pull in opposite directions. An inductor drags current behind the voltage; a capacitor pushes it ahead. That is why a capacitor bank cancels the lag of inductive loads, the basis of power-factor correction.

Coil first, then the capacitor

A coil makes current lag; a capacitor bank cancels it back to almost zero

Read it top to bottom. A clean sine feeds a resistive load with current riding exactly on voltage, PF 1.00. Add a coil and current is dragged behind by φ ≈ 58°, PF falls to 0.70. Switch in a capacitor bank and its leading current cancels most of that lag, pulling φ back to about 13° and PF up to 0.98, almost unity again.

What the meter sees

The power triangle, and what sets conductor loading

Real power P does the work; reactive power Q just sloshes back and forth. The grid, and the SEC meter, must carry the hypotenuse S. Raise the power factor and S collapses toward P.

The LED-driver twist

In phase, and still distorted

A bridge rectifier feeding a bulk capacitor draws current only at the crest of each half-cycle. Those spikes are packed with harmonics, so the true power factor sinks even when the phase shift is near zero.

The fix

Active PFC: a boost inductor reshapes the current

Active PFC switches a boost inductor thousands of times each cycle, forcing the input current into a clean sine locked to the voltage. That is how a good driver turns a 0.5 raw power factor into the 0.95+ on the datasheet, across the whole dimming range.

Key Takeaways

What you'll walk away with

Four ideas to carry into the next specification conversation you have.

Power factor = real power ÷ apparent power.

A PF of 0.95 means that 100 kVA supplies 95 kW of real power. It does not mean that the remaining 5% is a loss.

Lower PF requires more electrical capacity.

At the same voltage and real power, a lower PF requires more RMS current and apparent power. For applicable Saudi customers, PF below 0.95 also carries the SERA tariff charge.

Harmonics matter in LED drivers.

Phase displacement is only part of the story. Harmonic input current can reduce true PF even when the displacement factor is close to 1.0.

Specify the conditions, not only the number.

State true PF and THD_i under defined input voltage, load, temperature and dimming conditions, then request the corresponding test results.

Reference

Power factor × apparent power required

Apparent power required for every 100 W of real power. The calculation is S = P / PF.

PF	Apparent power per 100 W	Interpretation
1.00	100 VA	Unity power factor
0.95	105 VA	No power-factor charge at or above the current SERA threshold, where the tariff applies
0.90	111 VA	Below the SERA threshold for applicable customers
0.85	118 VA	More apparent power and RMS current required
0.70	143 VA	Substantially more electrical capacity required
0.50	200 VA	Twice the apparent power for the same real power

These values describe electrical loading. They do not represent percentages of useful light or direct energy losses.

IEC 61000-3-2:2018+AMD1:2020+AMD2:2024 specifies limits for harmonic-current emissions from applicable equipment tested under defined conditions. It does not establish a universal PF ≥ 0.90 and THD_i ≤ 15% requirement for every product. Those values are NLC project specification targets.
Source: SERA, Power Factor Tariff · Source: IEC 61000-3-2, Edition 5.2

Deep Dive

Real, reactive, and apparent, the triangle

Five ideas that turn PF from a number on a datasheet into a capacity decision.

The three powers, defined.

Real power, P, is the power converted into light, heat or motion. It is measured in W or kW. Reactive power, Q, is power associated with the cyclic exchange of energy between source and load through electric or magnetic fields, with no net energy transfer over a complete cycle. It is measured in var or kvar. Apparent power, S, is the product of RMS voltage and RMS current. It determines conductor and equipment loading and is measured in VA or kVA.

The cosine relationship, and its condition.

For sinusoidal voltage and current, power factor equals the cosine of the phase angle: PF = cos φ. For nonlinear loads such as many LED drivers, true PF also depends on current-waveform distortion. Under a sinusoidal supply voltage, true PF = displacement factor × distortion factor, and PF = cos φ / √(1 + THD_i²). A displacement factor of 0.95 with approximately 64% THD_i can produce a true PF of approximately 0.80.

Where it appears on a Saudi bill.

For customers subject to Saudi Arabia’s power-factor tariff, PF below 0.95 carries an additional charge of 5 halalas per excess kvarh. Applicability depends on the customer category and tariff conditions. Source: SERA, Power Factor Tariff

Passive and active PFC.

Passive PFC uses inductors and capacitors. Its performance varies with the circuit, load and operating point. Active PFC uses a switched converter to shape the input current so that it more closely follows the voltage waveform and contains less harmonic distortion. A well-designed active-PFC stage can maintain high true PF and lower THD_i across a defined operating range. The required limits and operating conditions must be stated in the product or project specification.

How to verify it.

Verify true PF and THD_i with a power analyser or power-quality analyser capable of measuring real power, apparent power and harmonic current under the specified operating conditions. A true-RMS current reading alone is not sufficient.

From the Academy to the Field

NLC Power & Control Systems, PF correction at the panel.

We design, supply and install MV/LV switchgear with automatic power-factor correction (APFC) banks sized to your actual harmonic profile.

See the solution

Shareable

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A 12-page explainer, ready to share as a LinkedIn document. The downloadable PDF and image set match the final approved version.

SLIDE 01

Power factor: why the same 100 W can demand more current

SLIDE 02

Same watts. More current.

SLIDE 03

Power factor is a ratio: PF = P / S = kW / kVA

12 pages · LinkedIn-ready. Download all 12 as high-res PNGs and post them straight to LinkedIn as a carousel. PDF version still available.

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Power factor, why 0.9 is not the whole story.