active components such as transistors. This difference makes it possible for APFs to mitigate a wide range of harmonics. The power conditioner will also have a "joule" rating. A joule is a measurement of energy or heat required to sustain one watt for one second, known as a watt second. Since electrical surges are momentary spikes, the joule rating indicates how much electrical energy the suppressor can absorb at once before becoming damaged itself. The higher the joule rating, the greater the protection. Uses Power conditioners vary in function and size, generally according to their use. Some power conditioners provide minimal voltage regulation while others protect against six or more power quality problems. Units may be small enough to mount on a printed circuit board or large enough to protect an entire factory. Small power conditioners are rated in volt-amperes (V·A) while larger units are rated in kilovolt-amperes (kV·A). Ideally electric power would be supplied as a sine wave with the amplitude and frequency given by national standards (in the case of mains) or system specifications (in the case of a power feed not directly attached to the mains) with an impedance of zero ohms at all frequencies. No real life power feed will ever meet this ideal. Deviations may include: Variations in the peak or RMS voltage are both important to different types of equipment. When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute, the event is called a "swell". A "dip" (in British English) or a "sag" (in American English – the two terms are equivalent) is the opposite situation: the RMS voltage is below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute. Random or repetitive variations in the RMS voltage between 90 and 110% of nominal can produce a flicker in lighting equipment. A precise definition of such voltage fluctuations that produce flicker has been subject to ongoing debate in more than one scientific community for many years. Abrupt, very brief increases in voltage, called "spikes", "impulses", or "surges", generally caused by large inductive loads being turned off, or more severely by lightning. "Undervoltage" occurs when the nominal voltage drops below 90% for more than 1 minute. The term "brownout" in common usage has no formal definition but is commonly used to describe a reduction in system voltage by the utility or system