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Busy Lamp Field (BLF) / Presence

The Busy Lamp Fields are generally the little LED lights on telephones that are associated with extensions.

How It Works


Every phone has different options for their BLF lights. Typically, a green BLF is associated with a free or available extension, a red BLF light is associated with a busy or otherwise unavailable extension, and a blinking red BLF light is associated with an extension that is ringing.

Practical Uses


  • Allow receptionists to immediately know if an extension is available to take a call without having to call the extension and possibly interrupt the destination with another call.
  • Often used by the staff to simply look at the phone to see if their colleague is available to speak.

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