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Abstract
In this paper I reviewed the effects that Compact Fluorescent Lamps (CFL), Light Emitting Diodes (LED), and halogen lighting have on power quality. The CFLs and some LEDs present a much greater non-linear load on the distribution system compared to incandescent lights, a common light source used in the past. The reason for the phasing out of the incandescent light was due to its poor efficiency compared to newer technology. A congressional bill was passed at the end of 2007 called the Federal Independence and Security Act which bans the manufacturing of the standard incandescent light bulb. As the less energy efficient incandescent bulbs are phased out, the new low energy lighting is being phased in, sometimes at the cost of power quality. As far as power quality is concerned, some low energy light choices are better than others.
Standard Lighting
Incandescent lamps provide an almost ideal resistive load at power line frequencies. A load that is totally resistive, with no reactance, results in a power factor of 1.00. This is an ideal condition allowing all current supplied by the distribution system to be consumed as real power by the lamp. For reference, the incandescent light bulb I tested actually consumed 102 watts (Figure 1). Graphs of power factor and harmonic magnitude with incandescent lamps are included as a control or reference to compare to low energy lighting (Figure 2). A resistive load will add very little harmonic distortion to the voltage waveform - any current distortion from the lamp is a reflection of the incoming voltage distortion.
Figure 1. Power factor measured on a 100 watt incandescent bulb with an Eagle 120
Figure 2. Harmonic magnitude measurement on a 100 watt incandescent bulb (above)
Halogen lamps are good replacements for standard incandescent light bulbs. Fundamentally, a halogen lamp is also resistive load- it’s a glowing filament like a traditional incandescent. On average, they consume 28% less energy compared to an incandescent bulb for the same light output. These bulbs have a great power factor of almost 1.00, as a resistive load (Figure 3).
Figure 3. Halogen lamp measuring a power factor of 1.00 with an Eagle 120
Halogen lamps are sometimes called quartz-halogen, quartz iodine, or tungsten halogen lamps. They are by definition an incandescent light that has a tungsten filament enclosed in halogen gas. When energized, a chemical reaction takes place that redeposits the evaporated tungsten onto the filaments. This chemical process increases the life of the bulb and allows the envelope to remain crystal clear for long periods of time. Due to their unique properties, halogens operate at a higher color temperature than standard incandescents and generate a higher luminous level using the same or less power input than a standard incandescent lamp. Because they are just a highly efficient incandescent lamp with a mainly resistive tungsten element, they present a resistive and not reactive load at power line frequencies. This property allows for the same ideal power factor and low harmonic distortion as a traditional bulb, with increased efficiency (in terms of light output per Watt), as shown in Figure 4.
Figure 4. Total Harmonic Distortion of 2.6% measured on a halogen lamp
Compact Fluorescent Lamps or CFLs are the worst offenders to power quality compared to halogen, LED, and Electron Stimulated Luminescence (ESL) lighting with a typical power factor of around 0.5 to 0.7, as shown in Figure 5. An example of their harmonic magnitude is shown in Figure 6. CFLs are very energy efficient, producing much more light with less power consumed. They also have the advantage of having a longer life than the incandescent lights they are replacing. They consume on average 75% less energy than the standard incandescent bulb for the same light output.
Figure 5. Power factor measured on a CFL
Figure 6. Harmonic magnitude of a CFL 100 watt equivalent lamp (above)
LEDs are diodes, and diodes are very non linear devices, but that is only a small part of the issue. LEDs are low voltage devices, and cannot operate directly from a 120V AC source. Each bulb includes a power supply that rectifies the AC to DC, and includes some type of voltage or current regulation. To maintain a high efficiency and small size, this power supply is usually an electronic switch mode power supply.
Many tradeoffs are involved in designing a mass-produced, small, efficient, but low cost LED power supply. A good design can include power factor correction, harmonic filtering, radio frequency interference (RFI) filtering, and resistance to voltage sags. A poor design may have little or no thought put towards these issues. The result can be high harmonics (leading to a high true power factor, even if the 60Hz power factor is still OK), RFI (leading to customer complaints to the utility about power line noise), and sensitivity to voltage flicker.
Several companies building LED lighting power supplies are beginning to realize the importance of power quality and are including a power factor correction circuit into their design. A block diagram of one such power supply is shown in Figure 7.
Figure 7. Block diagram for a power factor correction LED power supply
The manufacturer claims an outstanding true power factor of 0.99 while maintaining a high efficiency of 83% (measurement of .88 shown in Figure 8, grow lamp shown in Figure 9). This type of improved LED driver technology allows high efficiency lighting to comply with IEC 61000-3-2, an international standard on harmonic current limits. It ensures a more linear load allowing the power factor to be close to 1.00 and harmonics to be low (Figures 10 & 11).
Figure 8. Measurement of 0.88 power factor of an LED 100 watt equivalent lamp without the improved power factor correction circuitry
Figure 9. Power factor measurement on an LED grow light type flood lamp (above)
Figure 10. Total Harmonic Distortion of 45.6% measured on the LED 100 watt equivalent lamp (above)
Figure 11. Harmonic magnitude and THD measurement of the LED grow light (above)
Other Lighting
ESL, Electron Stimulated Luminescence lighting technology is a new use of an older idea. The ESL bulb works on the same principal as the old cathode ray tube in a television. An electron gun fires a spray of electrons at a phosphor coating on the inside of the bulb. The efficiency is comparable to that of a CFL, using about 70% less power than incandescent light bulbs. The power factor of the ESL bulbs is around 0.99, which makes them close to being a purely resistive load, similar to the incandescent light. At this time, LEDs beat them on efficiency by around 10% while maintaining a lower cost. Many consumers do not know about power factor and buy solely on price and efficiency, so in this case LEDs win. One advantage ESL has over CFL is that they can be used with a light dimmer.
Another lighting technology that is not normally used for home lighting, but may be used in the home to grow plants and are commonly used for street lighting is High Pressure Sodium (HPS) lighting. If the HPS ballast is not properly filtered, a large amount of harmonic current generated can be introduced into the distribution system. The harmonic content is so rich that HPS lighting can cause another issue- RFI. Public and street lighting commonly use HPS lighting, and much work has been done recently to improve performance by introducing an electronic control gear ballast. This new ballast type improves both power quality and efficiency at the same time.
For the purpose of taking control data, I used a standard 100 watt incandescent light bulb. The measurements were made using the PMI Eagle 120 receptacle PQ recorder. The two PQ measurements investigated here are the total harmonic distortion (THD) and true power factor. The THD quantifies the amount of current harmonic distortion introduced into the distribution system, while the true power factor is a measure of the overall power delivery efficiency (including reactive and harmonic effects).
Real power is the power that is being delivered to the load to perform work. Reactive power results from a net impedance of the load being either inductive or capacitive, resulting in stored energy either in a magnetic field of the inductance or electrostatic field in the dielectric of the capacitance that cannot perform work over a 60 Hz cycle. This reactive power, sometimes called wattless power, increases the RMS current that must be delivered through the distribution system, but performs no work. An example of the relationship between apparent, real, and reactive power is shown in Figure 12.
Figure 12. The Power Triangle- the relationship between Apparent Power (S), Real Power (P), and Reactive Power (Q) and how it relates to the phase angle
As described in the whitepaper Understanding How Harmonics Affect Power Factor, true power factor can be reduced by the presence of harmonics, or a reactive load. Either increases the RMS current (and thus the apparent power) without a corresponding increase in real power. Since the distribution system is burdened by the apparent power value, it is important to not only have a load that is efficient but also not reactive or rich in harmonics. An example is shown in Figure 13 of the reactance of a CFL putting the voltage and current out of phase.
Figure 13. Vector diagram showing how the reactance of the CFL put the voltage and current out of phase
At the present time, there are four major low energy lighting solutions to replace the old incandescent light bulb. The LED style is the most efficient, closely followed by the CFL, ESL and the Halogen styles. The LED-type bulb, if designed properly with the power factor correction circuitry, can be 80 percent more efficient than the 100 watt incandescent type and with a power factor as good as 0.99. The LED in this test consumed about 14 watts and had a power factor of 0.88 with a lumens output of more than 1600. This would make this LED bulb 86% more efficient than an equivalent incandescent lamp. The incandescent 100 watt bulb I used for a reference actually consumed 102 watts at the given line voltage, so I used this number as a reference to make the comparisons. The CFL I tested consumed 23 watts with a power factor of 0.64 and an output of 1600 lumens. The CFL tested was 77% more efficient than the incandescent. The halogen bulb consumed 72 watts with a power factor of around 1.00 and a lumen output of 1200; it was 29% more efficient than the incandescent lamp.
Conclusion
For power generation and distribution the amount of harmonic distortion and apparent power is of most importance. With higher volumes of CFLs introduced to replace the incandescent bulbs, even with the offset of the higher efficiency, the far-from-perfect power factor and THD of CFLs could be problematic. Even with today’s LED lamps, and a slightly better efficiency and power factor than with the older CFL lighting, the higher THD that they create can degrade power quality, causing issues to crop up that will need to be dealt with. Overall load from lighting may be smaller as these high efficiency bulbs are employed, but harmonic currents in an absolute sense are likely to increase, since traditional incandescents produced almost no harmonics. Technology that causes these issues can also be used to solve power quality issues. As high efficiency lighting continues to evolve, power factor correction and and harmonic filtering in each bulb may become more practical, and power quality may soon have a brighter future.
Cowles Andrus III
Communications Specialist
candrus@powermonitors.com
https://www.powermonitors.com
(800) 296-4120
