Dictionary of Electrical Engineering

Commonly used terms in the Electrical industry.

(1) a lateral on a primary distribution line is a short tap from the main distribution line which serves a local set of loads. Single phase laterals are common in residential districts.

(2) a three-phase or single-phase power line which supplies the distribution transformers along a street
See feeder
an elongated region of ionized gas that extends from one electrode to another just before a high-voltage breakdown.
the flux in a magnetic circuit that does not do any useful work.
leakage flux
the flux that does not link all the turns of a winding or in coupled circuits, flux that links one winding but not another. For example, the magnetic flux produced by the primary winding of a transformer that is not coupled to the secondary winding.
leakage reactance
the amount of inductive reactance associated with leakage flux. The leakage flux is the flux which traverses in paths farther from the designated paths such as the magnetic core in transformers and the air gap in electric machines and constitutes the non-useful flux. The electric circuit symbol of leakage reactance is Xl . It is a function of the leakage inductance and the frequency of operation. Higher values of leakage reactance affect the regulation and efficiency of the system. Xl is expressed in ohms.
See light emitting diode
left-hand circular polarization
the state of an electromagnetic wave in which the electric field vector rotates anticlockwise when viewed in the direction of propagation of the wave.
light emitting diode (LED)
a forward-biased p-n junction that emits light through spontaneous emission by a phenomenon termed electroluminescence.
light loss factor (LLF)
the ratio of the illumination when it reaches its lowest level at the task just before corrective action is taken, to the initial level if none of the contributing loss factors were considered.
light scattering
(1) spreading of the light as it passes or is reflected by an optically inhomogeneous medium.

(2) the process in which a beam of light interacts with a material system and becomes modified in its frequency, polarization, direction of propagation, or other physical property. See also spontaneous light scattering, stimulated light scattering, Brillouin scattering, Raman scattering. light valve See spatial light modulator.
lighting effectiveness factor (LEF)
the ratio of equivalent sphere illumination to ordinary measured or calculated illumination.
lighting system
any scheme used for illuminating a scene, usually for acquisition by a digital system. Illumination is crucial to digital images, since even illumination gradients that cannot be perceived by the eye can have an influence on the results of digital processing. For inspection tasks and document digitization, a uniform, reproducable, high level of lighting is usually required. Other applications have other requirements for uniformity, frequency, and intensity.

Structured lighting schemes are used to collect multiple images of a scene each having different illumination .

Strobe lights can be used to effectively freeze motion, and are useful for many visual inspection tasks.
See structured light
lightning arrestor
a voltage-dependent resistor which is connected in parallel with lightning-susceptible electrical equipment. It provides a low-resistance electrical path to ground during overvoltage conditions, thus diverting destructive lightning energy around the protected equipment.
lightning choke
one of several arrangements of conductors, usually a single or multi-turn coil, used to reduce lightning currents by increasing a power line's impedance at lightning frequencies.
(1) on a bus structure, one wire of the bus, which may be used for transmitting a datum, a bit of an address, or a control signal.

(2) in a cache, a group of words from successive locations in memory stored in cache memory together with an associated
tag, which contains the starting memory reference address for the group.

(3) a power-carrying conductor or group of conductors. line broadening nonzero spectral width of an absorbing or emitting transition; caused by many physical effects.
line conditioner
See power conditioner
line drop compensator
a multiply-tapped autotransformer equipped with a load-sensing relay which will adjust the line voltage to compensate for the impedance drop in the circuit between the device and the load center.
line impedance stabilization network (LISN)
a network designed to present a defined impedance at high frequency to a device under test, to filter any existing noise on the power mains, and to provide a 50 Ω impedance to the noise receiver.
line of sight (LOS)
the shortest possible straight line that can be envisioned, regardless of possible obstacles in the way, between a transmitter and a receiver. If a line of sight between transmitter and receiver is not blocked, the strongest signal will be received from the line-of-sight direction.
line outage distribution factor
a ratio used in contingency analysis. Given two parallel lines in a power system called x and y, assume that line y is removed from service. The line outage distribution factor of line x for the outage of line y is the ratio of the change in power flow on line x to the flow on line y before the outage.