Power Systems Engineering

Answer

The short answer is not necessarily. Power factor and efficiency measure two different things. The higher power factor light is easier on the electrical system, but that alone doesn’t tell you which light does a better job turning electricity into light. Let’s unpack why, because the distinction matters more than you might think.

Two different questions

Efficiency asks: how much useful output do I get for the real power I pay for? For lighting we call this efficacy, measured in lumens per watt (lm/W). That is the number that tells you which light is more efficient.

Power factor asks: how effectively does this load draw current from the system? It is the ratio of real power (watts) to apparent power (volt-amperes):

A PF of 1.0 means every volt-ampere delivered does real work. A PF of 0.8 means the system has to deliver 1.25 VA for every watt the light actually uses.

Notice that neither definition contains the other. A 0.8 PF fixture rated at 120 lm/W is more efficient at making light than a 0.95 PF fixture rated at 100 lm/W.

Let’s run the numbers

Take two LED lights, each consuming 10 W of real power on a 120 V circuit. Current is I = P ÷ (V × PF).

Light	Real power (W)	Power factor	Apparent power (VA)	Current (A)
Light A	10	0.95	10.5	0.088
Light B	10	0.80	12.5	0.104

Both lights use exactly the same real power. For a homeowner billed on kilowatt-hours, they cost the same to run. If they produce the same lumens, they are equally efficient.

But Light B draws about 19% more current to do the same job. That extra current is where power factor starts to matter.

What real lamp labels show

The math holds up on the shelf. Here are three standard A19 LED lamps on 120 V, using their published spec sheet data:

Lamp	Power factor	Real power (W)	Light output (lm)	Efficacy (lm/W)	Current at rated PF (A)
Satco S12143	0.95	9.5	800	84	0.083
PQL 91919	0.80	11	1,100	100	0.115
Satco S11417	0.76	9.5	800	84	0.104

The PQL lamp is the one to look at. At 0.80 PF it has the lowest power factor of the group, yet it is the most efficient at 100 lm/W, about 19% better than the 0.95 PF Satco. Its spec sheet also lists total harmonic distortion below 85%, a reminder that the distortion side of power factor is real.

The two Satco lamps make the opposite point. Same 9.5 W, same 800 lumens, same 84 lm/W, yet power factors of 0.95 and 0.76. They are equally efficient, but the 0.76 PF lamp draws about 25% more current.

One more thing worth noticing: the retailer listings show the same 0.079 A for both Satco lamps. That’s simply 9.5 W divided by 120 V, with power factor left out. Read the label carefully.

Efficacy for the Satco lamps and the current column are calculated from published watts, lumens and power factor. PQL efficacy is as stated on its spec sheet.

Where power factor really matters

One fixture won’t move the needle. A building with hundreds or thousands of them will.

• System losses. Conductor and transformer losses scale with the square of current (I²R). More current means more heat in the wiring and equipment upstream of the light, even though the light itself uses the same watts.
• Circuit and equipment capacity. Conductors, overcurrent devices and transformers are sized by amps and volt-amperes, not watts. Lower power factor means fewer fixtures per circuit and more transformer capacity tied up doing no useful work.
• The utility bill, for some customers. Residential customers generally pay for kWh. Many commercial and industrial customers also see demand charges based on kVA or penalties for low power factor, so the 0.8 PF light can cost them real money.
• Harmonics. With LED drivers, low power factor often isn’t a simple phase shift between voltage and current. It frequently comes from a distorted, non-sinusoidal current waveform. That distortion can add neutral current in three-phase, four-wire systems (triplen harmonics), cause extra heating and create power quality issues.

That last point is worth a pause. Power factor is really two factors multiplied together: displacement (the phase shift) and distortion (the waveform shape). Two lights with the same PF can get there in very different ways.

The bottom line

The 0.95 PF light is the better electrical citizen. It asks less of the wiring, transformers and utility to do the same work. But that doesn’t make it the more efficient light.

When you compare lights, look at both numbers for what they are:

1. Lumens per watt tells you which light is more efficient.
2. Power factor (and total harmonic distortion) tells you how that light behaves on the electrical system.

The best choice scores well on both. And the next time someone asks whether a higher power factor means higher efficiency, you’ll have a great opportunity to take them right to the edge of their next learning journey.