Episode 4 ~2:00 Electronics EN · العربية

Power factor, the 0.9 on your spec sheet, and the bill it pays for

Real power, apparent power, and the angle between them. Why a 0.95 driver beats a 0.85 driver on the SEC meter, and on the fixture count your building actually needs.

NLC Academy · Episode 4
Power Factor (pF)
~2:00
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 (kW) Reactive (kVAR) Apparent (kVA) φ
Real power does the work. Reactive power just shuttles back and forth. Apparent power is the current your wires actually carry.
The definition
pF= Real powerApparent power =cos φ
A pF of 0.95 means 95% of the current you draw does work. The other 5% just heats the wires.
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< 15%
Spec the threshold: demand > 0.9. Then verify it on site, cheap drivers drift below the line under load.
Why it lands on the SEC bill
kVA surcharge zone
105%0.95
111%0.90
118%0.85
143%0.70
200%0.50
Power factor →kVA drawn per 100 W of real power
SEC bills large customers on kVA, not just kWh. Lower power factor inflates kVA, and the penalty.
The phase angle
UNITYresistivePF = 1.0φφφLAGGINGinductivePF < 1φφφLEADINGcapacitivePF < 1VoltageCurrent
Power factor is the cosine of the lag between voltage and current
What each part does
Resistor V and I in phase PF = 1.0 Inductor (coil) current lags 90° lagging PF Capacitor current leads 90° leading PF
The coil makes current lag, the capacitor makes it lead
Coil first, then the capacitor
VoltageCurrent 1 · SOURCEresistive · in phasePF 1.00 φ = 0° 2 · + COILinductive · current lagsPF 0.70 φ ≈ 58° 3 · + CAPACITORleading I cancels the lagPF 0.98 φ ≈ 13°
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
φ Real power P (kW) Reactive Q (kVAR) Apparent S (kVA) corrected S, smaller PF = P / S = cosφ SEC bills large sites on apparent power S (kVA). Shrink φ and S shrinks onto P, the bill drops.
The power triangle, and why SEC bills the hypotenuse
The LED-driver twist
voltage current spikes The bulk capacitor only recharges near the voltage peak, so current arrives in narrow bursts, not a smooth sine. true PF = displacement × distortion
Even in step, a driver gulps current in spikes
The fix
AC mains 230 V Rectifier + bulk cap Active PFC boost inductor + switch shapes current to voltage LED string constant current input power constant DC to LEDs
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
UNITYresistivePF = 1.0φφφLAGGINGinductivePF < 1φφφLEADINGcapacitivePF < 1VoltageCurrent
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
Resistor V and I in phase PF = 1.0 Inductor (coil) current lags 90° lagging PF Capacitor current leads 90° leading PF
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
VoltageCurrent 1 · SOURCEresistive · in phasePF 1.00 φ = 0° 2 · + COILinductive · current lagsPF 0.70 φ ≈ 58° 3 · + CAPACITORleading I cancels the lagPF 0.98 φ ≈ 13°
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 why SEC bills the hypotenuse
φ Real power P (kW) Reactive Q (kVAR) Apparent S (kVA) corrected S, smaller PF = P / S = cosφ SEC bills large sites on apparent power S (kVA). Shrink φ and S shrinks onto P, the bill drops.
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
Even in step, a driver gulps current in spikes
voltage current spikes The bulk capacitor only recharges near the voltage peak, so current arrives in narrow bursts, not a smooth sine. true PF = displacement × distortion
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
AC mains 230 V Rectifier + bulk cap Active PFC boost inductor + switch shapes current to voltage LED string constant current input power constant DC to LEDs
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.

01

Power factor = real power ÷ apparent power.

Useful watts over total VA. A pF of 0.95 means 95% of the current you draw does work; 5% just heats the wires.

02

SEC bills on apparent power above a threshold.

Saudi Electricity Company charges large customers on kVA, not just kWh. Low pF inflates kVA, and the bill.

03

LEDs are not naturally good at pF.

A bare LED driver looks capacitive to the grid. A passive PFC stage pulls it back above 0.9; an active PFC pushes it above 0.95.

04

Demand > 0.9 in the datasheet. Verify on site.

Spec the threshold. Then measure at install with a power-quality meter. Drift below the line is common with cheap drivers under load.

Reference

Power factor × impact on your bill

Illustrative, actual penalty bands depend on customer category in the SEC tariff structure.

Power factor Effective vs nominal load Reference
1.00 (ideal, resistive)100% usefulIEC 60050
0.95 (active PFC driver)≈ 105% kVA per 100 W realIEC 61000-3-2 Class C
0.90 (typical good LED driver)≈ 111% kVA per 100 W realSEC threshold (large customers)
0.85 (passive PFC)≈ 118% kVA, surcharge zoneSEC tariff schedule
0.70 (uncorrected LED)≈ 143% kVA, heavy penaltyNot compliant
0.50 (legacy magnetic)≈ 200% kVA, unacceptableRejected at commissioning
Deep Dive

Real, reactive, and apparent, the triangle

Five concepts that turn pF from a number on a datasheet into a line item on a bill.

The power triangle, in one sentence.

Real power (kW) heats the room, lights the lamp, turns the motor. Reactive power (kVAR) shuttles back and forth between source and load doing no useful work. Apparent power (kVA) is the hypotenuse, the total current the wire must carry.

Harmonics matter as much as displacement.

Old textbooks frame pF as displacement angle (sine of φ). LEDs add a second sin, harmonic distortion. The full "true power factor" = displacement PF × distortion factor. A 0.95 displacement driver with bad THD can read 0.80 true.

SEC charges in kVA above 88 kW demand.

Saudi Electricity Company's medium-voltage tariff schedule (large commercial / industrial) bills both energy (kWh) and demand (kVA). A whole-building pF below 0.85 typically triggers a kVA penalty on every billing cycle.

Passive vs active PFC, and what each costs.

Passive PFC uses inductors and capacitors, cheap, bulky, gets you to ≈ 0.90. Active PFC uses a switched boost circuit, more expensive, more efficient, hits 0.95+ across the dimming range. For projects, active is the modern default.

Measure with a true-RMS meter, not a clamp multimeter.

A cheap clamp meter reports current magnitude but cannot resolve phase or harmonics. A power-quality analyser (Fluke 435, Hioki PW3198, etc.) returns real pF, harmonics, and per-phase data. Insist on this measurement at commissioning.

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
Next Episode

Choosing the Right Reflector

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An 11-slide explainer, ready to post straight to LinkedIn as an image carousel. Same content, faster reading.

Slide 1, Cover
SLIDE 01
Power factor, what you pay for vs what lights the room
Slide 2, The hook
SLIDE 02
Paying for watts you never use?
Slide 3, Definition
SLIDE 03
kW is real power, kVA is what the wire must carry

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