AV/IT Glossary—27 Days of #AVabc—L


LAN-Local Area Network—Supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.


Lambert—A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 foot-candles per square centimeter.

Lapping Film—Sheets of film used for polishing ferrule endfaces, comprising a film backing with mineral particles at various ratings for grit or coarseness.

Laser—A device that generates an intense beam of coherent monochromatic light (or other electromagnetic radiation) by stimulated emission of photons from excited atoms or molecules. Lasers are used in drilling and cutting, alignment and guidance, and in surgery; the optical properties are exploited in holography, reading bar codes, and in recording and playing compact discs.

Laser-Light Amplification by Stimulated Emission of Radiation—An optical source that generates coherent light within a narrow band of wavelengths.

Laser Chirp—A sudden change in the center wavelength of a laser, caused by reflected or crosstalk optical energy entering the lasing chamber.

Laserdisc—A format for storing analog video signals on a 12-inch double-sided disc.

Laser-Optimized Multimode Fiber—A multimode fiber with higher bandwidth than legacy multimode fiber, designed for transmission with laser based sources such as VCSEL.

Latency—A measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. In video processing or encoding products, it is a measure of the amount of time used to process an input signal. In a packetswitched network it is measured either one-way (the time from the source sending a packet to the destination receiving it), or round-trip (the one-way latency from source to destination plus the one-way latency from the destination back to the source).

Lavalier—A small microphone designed to be worn either around the neck or clipped to apparel.

Layer Li—A subset of the Audio part in the MPEG-1 and MPEG-2 standards. Some of its definitions are - 32-384 kbits/sec, sampling rates of 16-48 kHz etc.

Layer 2 Switch—Layer 2 switches support functions of the 2nd layer of the ISO model. Layer 2 switches provide hardware switching. They are capable of switching packets between devices connected to the switch. A table is built in the switch based on the physical MAC address of the connected devices. A Layer 2 switch does not examine IP packets.

Layer 3 Switch—Layer 3 functionality of the 3rd layer of the ISO model. They examine network packets and make switching and routing decisions based on information in the Ethernet packets. They are used in networked audio and video network delivery systems and large or complex internetworks, such as the Internet. Layer 3 switches support packet routing, VLANs and IGMP-snooping and multicast data stream delivery.

LBC-Laptop Breakout Cable—The Extron cable that connects a computer laptop to an Extron computer-video interface.

LCD-Liquid Crystal Display—A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between them. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing.

LCD projector—Utilizing LCD panel technology, these projectors separate the red, green, and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.

LCoS-Liquid Crystal on Silicon—This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry.

Lenticular Screen—A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.

Letterbox—A video image that results from displaying an image of widescreen aspect ratio on a television set of standard aspect ratio. The picture is presented between black bars above and below the image. Contrast with “windowbox.”

Level—The relative intensity of an audio or video source.

Level Control—The level control on some interface products is similar to the contrast control on a data monitor. It can either increase or decrease the output signal level from the interface to a data monitor or projector. This results in greater or less contrast in the picture.

LFE See “Low Frequency Effects”—Linear tracks The audio tracks recorded on VHS tape as thin stripes along the tape edge. Recorded and played back by a stationary head. The slow tape speed of VHS results in poor sound quality. Different from HiFi tracks, in which the audio is recorded along with the video by the spinning video head for higher audio quality.

Least Favored Viewer (LFV)—The farthest usable seat from the image. The LFV depends on the viewing angle toward the screen, image size, and content being displayed.

Lenticular—A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. Must be held very flat to avoid hot spots.

Lifespan—The technology life-cycle (TLC) describes the commercial gain of a product through the expense of research and development phase, and the financial return during its "vital life". Some technologies, such as steel, paper or cement manufacturing, have a long lifespan (with minor variations in technology incorporated with time) whilst in other cases, such as electronic or pharmaceutical products, the lifespan may be quite short.

Lifts—Lifts are designed to raise or lower equipment for easy access and storage as needed.

Light—The region of the electromagnetic spectrum that can be perceived by human vision, also known as the visible spectrum, which covers the wavelength range between about 0.4 µm to 0.7 µm. In laser and optical communications, this term denotes a broader portion of the electromagnetic spectrum, from the near-ultraviolet region of approximately 0.3 µm, through the visible region, and into the infrared region to 30 µm.

Light Emitting Diode-LED—A semiconductor device that emits incoherent, narrow-spectrum light within the p-n junction.

Light Level—The intensity of a given lighting situation as measured in foot-candles (Ft-c).

Light Source—In fiber optics, a generic for the optical signal transmitter in an optical loss test set - OLTS.

Lightguide—Also known as an optical waveguide or optical fiber, a glass or plastic fiber with the ability to guide light along its axis. It comprises a core at the center, surrounded by a cladding with a lower refractive index to keep the light within the core through total internal reflection.

Limiter—Audio circuit or device that prevents the signal from reaching a level where audible distortion can occur.

Line Compensation—Use of a video line amplifier/compensator (equalizer, EQ.) to pre-compensate for high frequency loss resulting from transmission of video signals over long cable distances (several hundred meters). Deterioration in the picture takes the form of loss of fine details and color distortion*. Sometimes the entire video signal, including sync* information, is severely attenuated. The analog line amplifier is usually installed at the beginning of the line. In the digital domain, a similar process is used – also called EQ., which employs high digital amplification stages and sometimes another process called reclocking, which is similar to analog TBC* operation.

Line Driver—A signal amplifier used to extend a video signal over extended distances. Similar in function to a distribution amplifier (DA), with one input and one output

Line Doubler—In its simple form, a device which converts a video signal to a high frequency computer DATA type signal. It is intended primarily for displaying video on a [[VGA]] monitor or on a DATA Wide Screen Projector An ADC is applied to the video signal, reading it into RAM* memory, adding lines and shifting the data to use high frequency scan rates as used by computers, and then passing the signal through a DAC in order to obtain an analog signal. The resulting image has higher quality and the sophisticated Doublers use Interpolation while adding lines in order to increase picture quality. A Line Quadrupler is an extension of a Line Doubler, adding even more lines to the video signal, displaying video on a 1024x768 or higher resolution monitor or projector. It does the opposite of a [[VGA]] to Video Scan Converter

Line Level—Audio signal industry-referenced at 600 ohms, 0 dB. Consumer systems may use a different reference.

Line Out—Audio output. In consumer systems, this may be 10,000-50,000 ohms, at -10 dB or -20 dB.

Line Up—A test signal recorded at the beginning of a tape, comprising an audio and a video signal, which is used as a reference for future recording and playback.

Line Voltage—Alternating current (AC) at the level typically found in the home.

Linearity—The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen but a different size when it is at the bottom of the screen.

Link—An optical cable with connectors attached to the transmitter and receiver.

Lip Sync—A technical term for matching lip movements seen in a video picture with voice. Audio and video is synchronised when lip sync is maintained.

Listening Plane—In acoustics, the intersection of the audio field (the horizontal plane) with the listener’s ear.

LNB (Low-Noise Blocking Converter)—A device inside a DBS dish that picks up the transmitted digital video signal.

Load Center—An electrical industry term used to identify a lighting and appliance panelboard designed for use in residential and light-commercial applications.

Load Resistance—The resistance impedance that a properly terminated cable places on the signal transmitted through it. In the case of a high frequency signal, signal-to-cable matching is essential to prevent signal deterioration. A specific load resistance (which is equal to the cable's characteristic impedance) should terminate the cable, which in video is usually 75 ohms. Improper cable loading results in signal distortion*, ghost images, color loss and other adverse phenomena. The source resistance should be equal to that of the cable's impedance and the load resistance.

Local Monitor—A device used to monitor the output of a signal from a system or other device in a local vicinity.

Localization—The ability to detect the directionality of sounds.

Logarithm—An exponent used in mathematical equations to express the level of a variable quantity (or, the power to which a number must be raised to produce a specific result).

Logo Generator—A machine used in broadcast and video production studios for generating a logo, to be displayed on the screen, usually in a specified corner. The logo, which is a graphic symbol, is usually stored on a ROM (Read Only Memory) chip and is keyed into the video picture upon request. Today, the classic generated logo has been replaced by a PC generated logo, encrypted into the video image using [[Genlock]] equipment. The computerized PC logo generator allows more flexibility in logo Generation and insertion, provides more graphic and eye-catching tools and is easier to use.

Loop-Through—A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording device(s). Loop-through connections are found on some scan converters and scalers. (Loop-out)

Looping—A term used to describe the cascading or chaining of a video signal to several video machines (distribution amplifiers*, VCRs, monitors, etc.). For example, a VCR is hooked up to a distribution amplifier, which has a video-input connector, and a loop output connector. When a signal is transmitted to the first machine through the input socket, it is fed, as an unprocessed signal, through the loop output connector (parallel connection) to the second machine. In turn, exactly the same signal is fed to a third device which is attached to the second one, and so on. Thus a very large number of VCRs or other video devices can be looped together for multiple processing. Proper signal terminations should be noted. In a large cascaded setup, signal termination is normally applied at the last machine in the chain.

Loose Buffer Cable—A type of fiber optic cable in which the fiber is encased within a loosely surrounded buffer tube underneath the jacketing. The tube is usually for protection in outdoor installations.

Loose Tube Gel Filled-LTGF—A Loose Buffer Cable that is filled with a insulating gel material.

Loss—In fiber optics, the loss of optical power in connectors, splices, and fiber defects as light passes through a fiber optic system.

Loss Budget—A specified, maximum tolerable loss of optical power, or attenuation of light, as it passes through a fiber optic system.

Lossless—When using compression to reduce text and/or graphic files, some techniques discard data in the process. Methods that compress files without losing data are called lossless.

Lossy—A term to describe compression techniques that throw away data as part of the process. The more data loss, the smaller the file, and the lower the quality (grainy or jagged edged) of the image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, high means high compression (greater loss) and low means low compression (less loss).

Lossy Compression—Method which discards (loses) some of the data, in order to achieve its goal, with the result that decompressing the data yields content that is different from the original, though similar enough to be useful in some way.

Loudness—The sound pressure level (SPL) of a standard sound. Loudness is the perception of the strength or weakness of a sound wave resulting from the amount of sound pressure level produced. Sound waves that have more intensity or larger variations in air pressure produce louder sounds. Low-intensity sound waves with smaller fluctuations in air pressure produce quieter sounds.

Loudspeaker—An electro-acoustic transducer that converts electrical audio signals at its input to audible sound waves at its output.

Low-Cut Filter—A circuit than removes bass frequencies from an audio signal. Also called a “highpass filter.”

Low Frequency Effects (LFE)—A separate channel in the Dolby Digital format reserved for low-bass effects, such as explosions. The LFE channel is the “.1” channel in a 5.1- channel format.

Low Impedance—The condition where the source or load is at a lower impedance than the characteristic impedance of the cable. Low source impedance is common; low load impedance is usually a fault condition. Example: 30-600 ohms.

Low Pass Filter—A circuit that discriminates between low frequencies and high frequencies and allows only the low frequencies to pass. For example, a low pass filter design for a subwoofer, set at 80 Hz, would allow the audio signals below 80 Hz to pass through to the speaker, and attenuate the portion of the signal above 80Hz.

Low Voltage—An ambiguous term. It may mean less than 70V AC to an AV contractor, while an electrician may use the same term to describe circuits less than 600V AC. The term may also be determined by the authority having jurisdiction (AHJ).

LPAC-Lossless Predictive Audio Compression—An improved lossless audio compression algorithm developed by Tilman Liebchen, Marcus Purat and Peter Noll at Institute for Telecommunications, Technical University Berlin (TU Berlin), to compress PCM audio in a lossless manner, unlike conventional audio compression algorithms which are lossy. It is no longer developed because an advanced version of it has become an official standard under the name of MPEG-4 Audio Lossless Coding.

LPCM-Linear PCM—A specific method of pulse code modulation that is used to represent an analog waveform as a sequence of amplitude values. LPCM has been defined as part of the DVD and Blu-ray Disc standards, and is also used by HDMI. Also see "PCM – Pulse Code Modulation."

LSFOH-Low Smoke and Fumes Zero Halogen—IEC designation of a cable jacket that passed IEC 332-3 flame test, IEC 61034 smoke test, and IEC 754-1 corrosivity test.

LTC-Longitudinal Timecode—Another system for encrypting Timecode on a tape (see Timecode*, VITC*). This system uses an audio track for Timecode recording.

Lucent Connector-LC—A high-density optical fiber connector becoming more popular and are replacing the popular SC due to the smaller size. LCs are used on Extron fiber optic products.

Luma—Also called Luminance. The photometric radiance of a light source. The luma signal represents brightness in a video picture. Luma is any value between black and white and is abbreviated as “Y.” Also see "Chroma."

Luma (luminance) Key—A picture-combining effect where the Y (luminance) portion of one video signal is replaced with video from another source. Luma keys are typically used to insert white text into a color video image.

Luma Delay—A video problem in which the intensity of an object or area is shifted slightly to the right of the color. The color occurs in the correct area of the displayed image, but the luma (intensity) starts later.

Luma Noise—Noise which manifests itself in a video picture as white snow*. It is the product of one or more of the following factors: low signal level due to poor lighting conditions, a poorly-manufactured video device, low quality video tapes, excessively long video cables used without pre-compensation, dirt on the video recorder heads which interferes with reading and writing, and over-enhancement of the video signal. Good quality video processors do not generate Luma noise. They maintain an excellent enhancement level, without sacrificing picture quality, by using noise gates*. Snow* can easily be reduced or eliminated in poorly recorded tapes and a clean copy can be created. In the digital domain, Luma noise may be a result of poor digitization processes, signal jitter (digital clock related problems), logic level incompatibility and similar voltage-related reasons.

Lumen—The unit of measure for light coming out of a light source, such as a projector. CRT projectors usually use a 10% white window pattern for measurement purposes, while LCD and DLP projectors use a 100% white window (ANSI standard). Also see "ANSI lumen."

Luminance—1) In physics, The light density coming out of a surface. This is the specification for measuring the brightness of a projection screen or a CRT monitors tube surface. The SI unit is cd/m2 (candles per square meter). It is also called nit in the US system and foot-lambert in the English system. 1 foot-lambert = 3.426 cd/m2. 2) In video technology, The measurement of the black to white value for a pixel.

Luminous Flux—The total amount of light coming from a light source, measured in lumens.

Lux—A contraction of the words luminance and flux; metric version of footcandle.

LVDS-Low Voltage Differential Signal—A signal transmission standard developed for the connection of laptop computers to their local LCD displays. National Semiconductor is the manufacturer that is promoting this standard. SGI used LVDS on the 320 and 540 NT Visual Workstations for connection to their 1600SW series, 16 x 9 aspect ratio, LCD monitor.

LXW-Lempel, Ziv and Welch—Compression and encoding method named after the inventors, which analyzes a file - even a color file, and reduces its size by checking redundancy of patterns.

Leave a comment

Please note, comments must be approved before they are published