expressed as THD limits for the current, calculated in the same way as for the supply voltage; for commercial and industrial lighting equipment, the THD limit is set at approximately 30 percent by ANSI standards. For fluorescent and HID lamp ballasts these limits are defined in ANSI C82.77-2002. The displacement of the current waveform is expressed in terms of PF, which is usually defined as the ratio of the real electric power flowing in the product to the apparent power.11 ANSI standards and other voluntary standards also define PF limits for lighting equipment, typically 0.9 for commercial and industrial equipment. These limits have been in place for several decades and, because of a lack of reported problems, seem to be appropriately set. There are currently no THD or PF standards for SSL products, so it would seem appropriate that similar limits be set for SSL drivers for commercial and industrial applications as for fluorescent ballasts. It should be noted, however, that, for residential lamps with integral ballasts and medium screw bases, ANSI C82.77-2002 specifies very loose standards—PF is required to be greater than 0.5 and THD less than 200 percent. Note, however, that the PF for an incandescent lamp is 1 (i.e., “perfect”) and its THD is 0. Therefore, the impact of the residential standard has been minimal as the penetration of screw-base CFLs is limited. As LED lamps become more ubiquitous as replacements for discontinued incandescent lamps, the effects of the liberal PF and THD limits may not be so benign. The ANSI standard for residential screw-base lamps should match that of commercial and industrial applications, as for fluorescent ballasts.

Modern lighting equipment, such as electronic ballasts for fluorescent lighting or drivers for SSL devices, also generate some electrical energy in the radio frequency bands. These types of equipment are termed unintentional radiators by the FCC, and the FCC sets limits for the conducted (i.e., along the electrical wires) and radiated (i.e., into the air) emissions of such equipment.12 Separate limits are set for residential and non-residential applications, with the residential limits being significantly stricter than non-residential ones, presumably to protect the consumer’s ability to receive AM radio broadcasts in the home.

In the European Union, the Low Voltage Directive (2006/95/EC) of the European Parliament sets limits for PF, THD, and radio frequency emissions for lighting equipment and does so by reference to standards published by the International Electrotechnical Commission (IEC) and the Comité International Spécial des Perturbations Radioélectriques (CISPR; in English, Special International Committee on Radio Interference). All of these limits are mandatory in member countries, and the PF and THD limits tend to be stricter in Europe (THD limits for current are in the range of 30 percent) than they are in the United States and apply to a broader class of lighting products, such as lighting controls. On the other hand, CISPR does not distinguish between residential and non-residential emission limits, and the European requirement falls between the FCC’s residential and non-residential limits. Other countries typically follow either the European model or the U.S. model.

Historically, there has been a tug of war between the electric utilities and the lighting industry about the importance of stricter limits on power quality metrics, in particular on THD and PF, because of concerns about incompatibility between an increasing number of electronic loads in buildings. However, the reported number of incidents claiming poor performance because of power quality problems has remained low, while the number of installed electronic ballasts has increased. Electronic ballasts, introduced to the market in the 1980s, now account for more than 80 percent of sales of all linear fluorescent lamp ballasts in the United States. The current limits, therefore, appear to be appropriate.

FINDING: There are existing standards for THD and PF for electronic ballasts for linear fluorescent lamps, but at present there are no such residential standards for LED drivers that are external to the lamp. Standards for low-wattage, integrally ballasted CFLs with medium screw bases in residential applications allow low PF and high THD.

RECOMMENDATION 4-5: For external solid-state lighting drivers in general, industry should adopt the same total harmonic distortion and power factor standards that are in place for electronic ballasts for linear fluorescent lamps. Industry should revisit the standards for low-wattage medium screw-base lamps to determine their impact on power quality before applying them for light-emitting diode lamps, and these standards should match those for commercial and industrial applications.


A recent limited survey of consumer prices for a variety of lamp types (A19, MR16, PAR20, and PAR38) at a Home Depot store in New Jersey indicates that the initial cost of LED lamps ranges from 3.5 times to 15 times (PAR38) that of halogen lamps (PAR20). However, when the total cost of ownership is calculated using an electricity rate of


11 The power factor (PF) of the equipment is equal to the electric power dissipated in the equipment expressed in watts divided by the product of the amplitude of the supply voltage and the amplitude of the electric current drawn by the equipment expressed in volt-amperes. In the past when most ballasts used in lighting were magnetic coils, the main effect to reduce PF came from the phase angle difference between the supply voltage and the current drawn by the equipment, which is why PF can be thought of as the displacement of the current relative to the voltage. With modern electronic ballasts this effect is smaller, and increasing THD also decreases PF. For example, in the absence of any displacement PF, a THD of about 44 percent corresponds to a PF of 0.9. PF is of particular interest to the electric utilities because they bill their customers based on delivered real power. However, the transmission line capacity is expressed in terms of amperes of current, so a low PF product will limit the utility’s ability to generate revenue.

12 47 CFR Part 15 and 47 CFR Part 18.

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