CCTV Glossary
Cascadia Video Products LLC
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L
Lambertian source or surface - A surface is called a Lambert radiator or reflector (depending
whether the surface is a primary or a secondary source of light) if it is a perfectly diffusing surface.
LAN - Local Area Network. A short distance data communications network (typically within a
building or campus) used to link together computers and peripheral devices (such as printers, CD
ROMs and modems) under some form of standard control.
Laser - Light amplification by stimulated emission of radiation. A laser produces a very strong
and coherent light of a single frequency.
LED - Light Emitting Diode. A semiconductor that produces light when a certain low voltage is
applied to it in one direction.
Lens - An optical device for focusing a desired scene onto the imaging device in a CCTV camera.
Level - When relating to a video signal it refers to the video level in volts. In CCTV optics, it refers
to the auto iris level setting of the electronics that processes the video signal in order to open or
close the iris.
Line-locked - In CCTV, this usually refers to multiple cameras being powered by a common
alternative current (AC) source (either 24 V AC, 110 V AC or 240 V AC) and consequently have
field frequencies locked to the same AC source frequency (50 Hz in CCIR systems and 60 Hz in
EIA systems).
Liquid crystal display (LCD) - A screen for displaying text/graphics based on a technology called
liquid crystal, where minute currents change the reflectiveness or transparency of the screen. The
advantages of LCD screens are very small power consumption (can be easily battery driven) and
low price of mass-produced units. The disadvantages are narrow viewing angle, slow response
(a bit too slow to be used for video), invisibility in the dark unless the display is back lighted, and
difficulties displaying true colors with color LCD displays.
Lumen [lm] - A light intensity produced by the luminosity of 1 candela in one radian of a solid
angle.
Luminance - Refers to the video signal information about the scene brightness. The measurable,
luminous intensity of a video signal. Differentiated from brightness in that the latter is
nonmeasurable and sensory. The color video picture information contains two components,
luminance (brightness and contrast) and chrominance (hue and saturation). The photometric
quantity of light radiation.
LUT - Look-up table. A cross-reference table in the computer memory that transforms raw
information from the scanner or computer and corrects values to compensate for weakness in
equipment or for differences in emulsion types.
Lux [lx] - Light unit for measuring illumination. It is defined as the illumination of a surface when
luminous flux of 1 lumen falls on an area of 1 m2. It is also known as lumen per square meter, or
meter-candelas.
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