The CCTV Glossary
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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 aperfectly
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, file servers and modems) under some form of standard control.
Laser.  Light Amplification by Stimulated Emission of Radiation.  A laser produces a very
parallel and coherent light (all wave fronts in phase) of a single frequency.
LED.  Light Emitting Diode.  A semiconductor diode, that produces light when a certain low
voltage, forward bias, is applied to it.  Like a normal diode it conducts only in one direction.
Lens.  An optical device for focussing 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).
LCD.  Liquid Crystal display.  A screen for displaying text/graphics based on a technology
called liquid crystal, where minute currents change the reflectiveness or transparency of the
by changing the polarization angle.  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, invisibility in the dark unless the
display is back lighted, and difficulties displaying true colors with colour LCD displays.
Lumen [lm].  A light intensity produced by the luminosity of 1 candela in one radian of a solid
angle (steradian - sr).
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 non-measurable and sensory.  The colour video picture information contains
two components, luminance- Y (brightness and contrast) and chrominance - C (hue and
saturation).
Look-up table.  A cross-reference table in the computer memory that will return an output
value for any given input value.  It can be a programmed algorithm or data entered in a table.
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 lumens per
square metre.  One lux is equal to approximately 0.09290 foot candle.
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