The power factor is an important specification to consider when selecting LED lights. It refers to the ratio between the real power drawn by the LED (in watts) and the apparent power provided to it (in volt-amps). The power factor indicates how efficiently the LED converts the supplied voltage and current into useful light output.
What is Power Factor?
Power factor is represented as a number between 0 and 1. A power factor of 1 means the voltage and current are perfectly in sync, so all the power being supplied is being converted to useful output. A power factor of 0 means the current and voltage are completely out of sync so no power is being usefully consumed. Most LED lights have a power factor between 0.9 and 0.99.
The power factor measures how much of the apparent power drawn from the supply is actually usable real power. Apparent power is the product of the voltage and current supplied, measured in volt-amps (VA). Real power is the power that actually powers the LED, measured in watts (W).
For example, if an LED draws 0.2 Amps of current from a 120 Volt supply, the apparent power is 120 x 0.2 = 24 VA. If the LED has a power factor of 0.9, the real power being used is 0.9 x 24 = 21.6 Watts.
Why Does Power Factor Matter?
A lower power factor means the LED driver has to draw more current to power the LEDs. This increased current can lead to higher energy loss in the system and require larger gauge wires. A higher power factor is desirable because it draws less current for the same useful light output.
For commercial installations, utilities often charge businesses extra if their electrical system has a low overall power factor. So using LED lights with higher power factors can help reduce utility costs.
The power factor can also impact the usable life of an LED product. LEDs with lower power factors tend to run hotter which degrades the components faster. LED lights with a high power factor produce less heat so they tend to have a longer rated lifespan.
Typical Power Factor Values for LEDs
Most quality LED lights have a power factor of 0.9 or greater. Here are some typical power factor values for different types of LED products:
- LED Bulbs: 0.9 to 0.95
- LED Downlights: 0.9 to 0.99
- LED Strips: 0.9 to 0.98
- LED Panel Lights: 0.95 to 0.99
- LED High Bay/Low Bay Lights: 0.95 to 0.98
- LED Street Lights: 0.90 to 0.98
Higher end LED fixtures designed for commercial use often have power factors of 0.95 or higher. Lower quality LED lights may have power factors below 0.9.
Reading the Power Factor on LED Packaging
For packaged LED bulbs and fixtures, check the markings printed on the packaging, spec sheet, or product description online. The power factor rating should be clearly listed along with other specs like lumens, wattage, voltage, etc.
As an example, a typical LED bulb may be rated as:
- 8W (8 watts power consumption)
- 900 lumens (light output)
- 120V (voltage)
- 0.95 PF (power factor)
For commercial LED tube lights, power factor may be marked directly on the tube along with other ratings. If not provided, check manufacturer spec sheets for the power factor.
Measuring Power Factor
For installations using multiple LED fixtures, the overall power factor can be measured with a power quality meter. This will measure the power factor for the combined load, which gives a system-wide reading. A low overall power factor may indicate issues with wiring, LED driver design, or overloaded circuits.
Some advanced LED drivers allow adjusting the power factor output. This is done by changing the capacitance settings in the driver’s input stage. Lower capacitance shifts the driver’s power factor closer to 1, which improves the unit’s efficiency. However this must be done carefully to remain within safety and design regulations.
Improving Low Power Factor on LED Systems
If an LED installation has a low overall power factor, here are some steps that can help improve it:
- Use LED products rated for higher power factors
- Replace older LED drivers with newer constant-current drivers
- Reduce overall load on circuits
- Balance load across phases for 3-phase systems
- Install power factor correction capacitors
- Rewire with larger gauge cables to reduce loss
- Have a qualified electrician inspect and tune the electrical system
Achieving a high power factor may require trading off features like dimming capability and color quality. Work with a lighting designer to determine the optimal power factor target for your unique needs.
Power Factor vs Efficiency
While related, power factor and efficiency are two distinct specifications for LEDs. Power factor measures how effectively the LED converts apparent power (volt-amps) to real power (watts). Efficiency measures how much of the electrical input power is converted to light output.
An LED may have a high power factor, but poor efficiency if much of the power is converted to heat instead of light. Conversely, a very efficient LED may still have a low power factor if the current and voltage are out of phase.
The product of efficiency and power factor gives the “displacement power factor” – this measures how much of the apparent power drawn from the supply ends up as useful light. Most quality LEDs have displacement power factors higher than 0.9.
Power Factor vs THD
Total harmonic distortion (THD) is another power quality metric related to power factor. THD measures the degree of distortion to the current waveform. Higher harmonics can negatively impact the power factor.
LED drivers with better THD performance generate cleaner current waveforms. This helps improve power factor. LED lights with both high power factor and low THD achieve maximum efficiency with minimal grid impact.
Conclusion
The power factor essentially indicates how efficiently an LED converts electrical current to useful light output. A higher power factor is desirable, with most quality LEDs rated for 0.9 or greater. Checking the power factor helps ensure optimal LED performance, lifespan, and energy savings.
When designing an LED lighting system, also pay attention to overall power factor for the combined load. Improving low system power factor through better LED selection, wiring, and drivers can lead to significant efficiency gains and utility cost savings.
Power factor is a key metric, but also consider related specifications like efficiency, THD, displacement power factor and color quality when selecting LED products and designing lighting systems.
Through careful selection of high quality LED lights and drivers, lighting designers can maximize both energy efficiency and power factor for commercial, industrial and residential applications.
Power factor gives valuable insight into how effectively an LED product or system converts supplied power into useful illumination. Check power factor ratings, and aim for values of 0.9 or higher for optimal LED performance.
Frequently Asked Questions
What is a good power factor for LED lights?
A power factor of 0.9 or higher is considered good for most LED lights. Values above 0.95 are optimal for commercial installations. High quality LED fixtures will have power factors from 0.95 to 0.99.
Why do LED drivers lower power factor?
The AC to DC conversion process in LED drivers causes the current to go out of phase with the voltage, which reduces the power factor. Advanced drivers use techniques like input filtering and power factor correction to minimize this effect.
Do LED lights with a lower power factor use more electricity?
Yes, a lower power factor means an LED will draw more current to produce the same light output. The increased current requires more power, results in resistive losses, and generates excess heat which can shorten the LED’s lifespan.
Does power factor affect LED brightness?
No, the power factor itself does not affect LED brightness or light output. Power factor only measures how efficiently the LED converts electrical current to light. An LED can produce full brightness even with a low power factor, but it will draw more power to do so.
How can I improve low power factor in an LED system?
Strategies to improve low system power factor include using better LED drivers, reducing load, rewiring with thicker cables, balancing multi-phase loads, installing power factor correction capacitors, and upgrading LED fixtures to higher power factor models.
Is power factor the same as Watts?
No, watts measure real power while power factor is a ratio between real power and apparent power. An LED’s wattage rating reflects how much power it consumes. Power factor measures how efficiently the supplied power is converted to light output.
LED Power Factor Tables
Here are some reference tables showing typical power factors for different types of LED lights:
LED Bulb Power Factors
| Bulb Type | Typical Power Factor Range |
|---|---|
| A-Shape LED Bulbs | 0.90 – 0.95 |
| MR16 LED Bulbs | 0.90 – 0.98 |
| BR30 LED Bulbs | 0.92 – 0.97 |
| PAR LED Bulbs | 0.90 – 0.98 |
| T8 LED Tubes | 0.90 – 0.94 |
| LED Globes | 0.92 – 0.96 |
LED Fixture Power Factors
| Fixture Type | Typical Power Factor Range |
|---|---|
| LED Panels | 0.95 – 0.99 |
| LED Downlights | 0.92 – 0.99 |
| LED High Bay | 0.95 – 0.98 |
| LED Troffers | 0.95 – 0.99 |
| LED Strip Lighting | 0.90 – 0.98 |
| LED Flood Lights | 0.95 – 0.98 |
Higher CRI (color quality) LEDs tend to have slightly lower power factors. But well-designed drivers can still achieve high power factor along with excellent color rendering.
LED Driver Power Factors
LED driver design has a major impact on power factor. Here are some typical power factor ranges for different driver topologies used in LED lighting:
| Driver Type | Typical PF Range |
|---|---|
| Linear LED Driver | 0.55 – 0.70 |
| Conventional LED Driver | 0.85 – 0.95 |
| Power Factor Corrected Driver | 0.95 – 0.99 |
Advanced LED drivers using power factor correction (PFC) circuitry can achieve power factors close to unity, maximizing efficiency.
Power Factor Requirements
Many rebate programs and commercial LED installations now require minimum power factor levels. Here are some common requirements:
| Agency/Program | Minimum PF Required |
|---|---|
| ASHRAE 90.1 | 0.90 |
| IECC | 0.90 |
| Energy Star | 0.90 |
| UL Type A Drivers | 0.90 |
| UL Type B Drivers | 0.50 |
| NEMA Premium Drivers | 0.90 |
| DLC Premium List | 0.90 |
Check your local utility incentives and commercial lighting regulations to determine required power factor levels for your LED application.
Measuring LED Power Factor
A power quality analyzer or power meter can measure power factor by simultaneously monitoring the voltage, current, real power and apparent power. Handheld meters are available for single fixture measurement. More advanced systems can monitor a whole panel or lighting circuit.
To measure power factor:
- Connect meter to power source and load (LED fixture)
- Allow LED to operate at full brightness
- Meter will measure current, voltage, real power (W) and apparent power (VA)
- Power factor is calculated as: PF = Real Power (W) / Apparent Power (VA)
A low power reading indicates poor power factor. Target greater than 0.9 for best results.
Improving LED Power Factor
If an LED fixture or lighting system has low power factor, here are some ways to improve it:
- Use LEDs and drivers with higher power factor ratings
- Reduce overall load on circuit
- Balance multi-phase loads equally
- Use larger gauge supply wiring
- Install power factor correction capacitors
- Upgrade old magnetic ballasts to LED drivers
- Replace CFLs and linear fluorescents with LEDs
- Optimize driver settings including input capacitance
Consulting a qualified electrical engineer can help correct persistent low power factor issues.
Power Factor vs Efficiency
Power factor measures how completely apparent power is converted to real power. Efficiency measures how much of the input power is converted to useful light output. They are separate but related metrics.
Power factor focuses on the phase alignment between current and voltage. Efficiency focuses on minimizing losses. It is possible to have high power factor but low efficiency if excess power is converted to heat instead of light.
The optimal LED lights have both high power factor (0.9+) to minimize reactive power and high efficiency (100+ lumens per watt) to maximize light output.
Conclusion
In summary, power factor is an important LED performance metric that measures how efficiently the LED converts electrical current to light. Values of 0.9 or greater are recommended for optimal efficiency and longevity.
Check manufacturer specs, install power meters, and work with lighting designers to maximize power factor. High power factor LEDs consume less power, generate less heat, and last longer.
While power factor focuses on phase alignment between current and voltage, also consider efficiency which measures light output per watt. The best LED solutions maximize both power factor and luminous efficiency.