Definition
Power Factor (PF) is the ratio of real power (watts, doing actual work) to apparent power (volt-amperes, the total electrical load the wiring must carry). PF ranges from 0 to 1 — PF 1.0 means all current is doing useful work; PF 0.5 means 50% of the current flowing through the wiring is wasted as reactive power. Low power factor is caused by inductive or capacitive loads (like LED driver input stages) that draw current out of phase with voltage. A PF 0.5 LED driver draws twice the current of a PF 1.0 driver for the same wattage — overheating wiring, reducing the number of fixtures per circuit, and potentially incurring utility penalties. IEC 61000-3-2 mandates PF ≥0.9 for lighting equipment >25W (Class C), and Energy Star requires PF ≥0.7 for residential and ≥0.9 for commercial luminaires.
Key Data
| Parameter | Value / Explanation |
|---|---|
| PF 0.95-1.0 | Excellent — premium LED drivers with active PFC (Power Factor Correction). Near-unity PF. |
| PF 0.90-0.95 | Good — meets IEC 61000-3-2 Class C for >25W. Standard commercial grade. |
| PF 0.70-0.90 | Acceptable — typical of budget LED drivers without active PFC. Fine for <25W residential. |
| PF 0.50-0.70 | Poor — causes excessive current draw, circuit overload risk, potential utility penalties. |
| PF <0.50 | Unacceptable — avoid for any commercial/industrial application. Indicates severe design flaw. |
| THD (Total Harmonic Distortion) | Related metric — should be <20% per IEC 61000-3-2 Class C. High THD causes neutral conductor overheating in 3-phase systems. |
Application Guide
Large office (300+ fixtures)
PF ≥0.95, THD <10%, active PFC driver
At scale, PF 0.5 vs 0.95 is the difference between 15 and 7.9 circuits — significant electrical infrastructure cost
Residential (single fixture)
PF ≥0.7 acceptable, PF >0.9 preferred
Single fixture impact is negligible; grid-level harmonics are the concern
Industrial (1,000+ high bays)
PF ≥0.95, mandatory — check utility tariff for PF penalties
At megawatt scale, PF 0.5 would cost ~$15,000/year in utility penalties plus require oversized transformers
Conclusion & Procurement Recommendation
For B2B LED procurement, always specify power factor in driver requirements — it's a hidden cost multiplier. Key specifications: (1) PF ≥0.95 at full load for projects >100 fixtures, (2) PF ≥0.9 at 50% dimming level (many drivers maintain high PF at full load but drop to 0.5 when dimmed — specify PF across the full dimming range), (3) THD <15% (IEC 61000-3-2 Class C limit) to prevent neutral conductor and transformer overheating, (4) For 3-phase installations, specify balanced phase loading and verify PF per phase. Request driver datasheets showing PF vs load curve and THD spectrum. Budget drivers typically omit active PFC, resulting in PF 0.5-0.7 — the $2-5 saved per driver costs 10× more in electrical infrastructure.