Why is the power factor of home lighting only 0.5, while that of engineering lighting must be ≥0.9?

You may have noticed a strange phenomenon:

• When buying home LED lamps at a lighting store, the data sheet often lists a power factor (PF) of around 0.5.
• But when it comes to construction projects, bidding documents and acceptance criteria require lighting systems to have a PF ≥ 0.9.

Is this cutting corners? Or is it the dividing line between good and bad quality?

Neither—it's the result of a balance of technical, regulatory, and economic factors.

1. First, let's clarify: What is power factor?

Let's skip the formula and use a beer glass as an analogy:

• Beer = Active Power (Electricity that actually does useful work)
• Foam = Reactive Power (Electricity that doesn't directly do work, but is needed for circuit operation)
• The capacity of the entire glass = Apparent Power (The total capacity the grid has to provide for you).

Power factor (PF) = beer / total cup volume.

A high PF means less foam; a low PF means more foam, and the grid works hard for a long time before you get half a cup of "real electricity."

In electronic devices like LED lights, the biggest culprit for low PF isn't traditional "phase difference" but harmonic distortion. This occurs when the current waveform is "sharpened" by the rectifier circuit, causing the current to only sip at the peak voltage, much like a person only sipping water when the straw is held to the surface. The result is a frothy, naturally low PF.

2. Regulations: Residential and industrial lighting follow different "tracks."

The international standard IEC 61000-3-2 (GB 17625.1) regulates lighting equipment according to different power levels:

• >25W (mostly commercial/industrial lighting): Strict harmonic limits apply, essentially requiring the use of active power factor correction (APFC) circuits, with a PF of ≥0.9.
• 5–25W (most household light bulbs): The standard provides a relaxed compliance option, allowing compliance without PFC, with a PF of ≈0.5–0.6.
• ≤5W: Almost exempt, regardless of harmonics.

China's standard system is consistent with the international one, but there are also engineering design standards (such as "GB50034 Architectural Lighting Design Standard") that require the system PF ≥ 0.9, which forces engineering lights to choose high PF products.

Simply put:

• Home renovation: Check individual lights; as long as they comply, there's no hard and fast PF requirement.
• Engineering: Check the entire system; the PF must be ≥ 0.9; otherwise, the system will fail acceptance.

3. Technology: PF is inherent in the circuit design and cannot be adjusted arbitrarily.

Three Common LED Driver Topologies:

1. No PFC (PF ≈ 0.5–0.6): The cheapest option, using a rectifier and large electrolytic capacitors, is standard for household lighting.
2. Passive PFC (PF ≈ 0.7–0.8): Adds several diodes and small capacitors to improve the waveform, but costs slightly more.
3. Active PFC (PF ≥ 0.9): Adds a PFC control chip, an inductor, and a MOSFET. The current waveform is nearly synchronized with the voltage. This option is the most expensive and is standard for industrial lighting.

Key point: PF is a "by-product" of the topology structure. The PF is almost determined by the circuit selected during design.

4. Economic Considerations: Home renovations focus on "unit price," while construction projects focus on "TCO."

• The home renovation market is extremely price-sensitive. Regulations allow for low PFs, so manufacturers naturally use the cheapest solution. Residential electricity bills are metered based on active power, so a low PF has little impact on the bill.
• Engineering Market:

1. 1. Regulatory requirements: A power factor (PF) of ≥ 0.9 is the entry threshold for projects.
   2. Operating Costs: A high power factor reduces line losses, avoids fines, and reduces distribution capacity.
   3. Safety: A low power factor makes the distribution system more susceptible to overheating and overload.

For the same 100W load, the loop current is nearly halved when the PF is 0.9 compared to 0.5. This is the fundamental reason why engineering projects insist on high PF.

Therefore:

• A PF greater than 0.5 for residential lighting is the most cost-effective solution;
• A PF ≥ 0.9 for engineering lighting is a result of both regulatory and economic considerations.

5. Recommendations for Different Users

• Home users: When purchasing lamps, don't worry about PF (light pulsation factor)as long as it’s complied with regulations. Focus on color rendering, luminous efficacy, and safety.
• Engineering/Design: A PF of ≥ 0.9 should be included in bidding documents and specifications, and spot-tested during acceptance to prevent low-PF lamps from being introduced into project systems.

6. Summary in One Sentence

PF>0.5 and PF≥0.9 are not about quality, but rather the optimal choice under two different markets, two different sets of regulations, and two different economic logics.