Video Surveillance Glossary of Terms [K - L]

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• » LAN (Local Area Network) [top]
  A LAN is a high-speed network connecting computers that are nearby (probably in the same building), and offers differing connection protocol options.
  
• » Latency [top]
  The speed of a network is dependent on both latency and bandwidth, with latency referring to the time needed for an IP packet to travel from source to destination.  Wide bandwidth and low latency are preferable.
  
• » LED (Light Emitting Device) [top]
  Monochrome surveillance cameras use LEDs to provide infrared light.  An LED creates an infrared light frequency when stimulated by an electric charge. 
  
• » Lens [top]
  This is the device responsible for focusing the image on the CCD, and most offer adjustable focal length and aperture.
  
• » Level control [top]
  Level control is control of the main iris, and sets the auto-iris circuit to a specific video level of the user’s choice.  The iris is therefore set to maintain this video level no matter what the light condition may be.  A high level opens the iris; a low level closes it.
  
• » Light sensor [top]
  Often used to turn infrared illuminators on or off, this device is triggered when it detects a pre-set amount of light, and helps cope with low (or no) level light conditions.
  
• » Limit switch [top]
  A security camera’s pan and tilt head with one of these devices installed (either inside or outside it) is limited in the angles it can move. 
  
• » Linux [top]
  Linux is an open source UNIX implementation, and a popular alternative to the Windows operating system.  It is often used in embedded operating systems found in advanced Network IP Cameras.  Linux is freeware.
  
• » Loss Prevention [top]
  Best summarized as ‘not having anything stolen’, loss prevention is the practice of securing devices or information from theft or loss.  Video surveillance is a common practice in preventing theft or other losses of property like vandalism.
  
• » Lumen [top]
  A lumen (abbreviated as lm) is a unit that measures the visible power output of a light.  While watts measure the power the bulb needs, lumens measure the visible light that the bulb generates.
  
• » Lux [top]
  Used more often than lumens when discussing security cameras, a lux is a unit of illumination. It measures the amount of uniform light that falls on one square meter (expressed in one lumen per square meter).  Security camera specs use the lux to indicate how much light they require to operate, with lower lux levels indicating a camera as more effective in lower ambient light.  Look for 0.2 lux or less when choosing a low-light camera, and 2 lux or higher for daylight cameras.

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