What Is a Busy Lamp Field (BLF) on a Business Phone?
A busy lamp field (BLF) is a set of lights on your desk phone that show whether colleagues are free, ringing or on a call. Press a lit key to call that person, or to pick up their call if it is ringing and they are away from their desk.
How does a busy lamp field work?
Each BLF key is assigned to a colleague’s extension. The phone keeps an eye on that line and changes the light when its status changes. The same key doubles as a speed dial, so one press rings the person when they are free.
| Light | Usually means | Pressing the key |
|---|---|---|
| Unlit or steady green | The line is free | Calls that colleague, or starts a transfer |
| Steady red | The colleague is on a call | Usually does nothing useful. Wait, or choose someone else |
| Flashing red | The colleague’s phone is ringing | Picks up their call (if pickup is allowed on your system) |
Colours and flash patterns vary by handset and system, so check the guide for your model.
What is a BLF used for?
- Transfers without guesswork. You can see a colleague is free before you send a caller to them.
- Picking up ringing calls. If someone is in a meeting, a nearby colleague answers without shouting across the office.
- Reception cover. A receptionist can watch the whole team on one handset.
- One-touch dialling. The key is also a speed dial for the people you ring most.
What are the limits of a BLF?
Not every phone supports it (see Gamma Horizon and 3CX for the platforms we support), and the number of keys depends on the handset. On Gamma Horizon, the maximum is 50 busy lamps when a sidecar (an expansion unit with extra keys) is fitted, and the portal checks your phone is compatible before it lets you set one up. There is also a privacy angle. A BLF shows a colleague’s line status, so decide who should be able to see whom.
How is a BLF different from a call pickup group?
A pickup group lets anyone in the group answer any ringing phone in that group. A BLF lets you choose the specific person you are watching and covering. Many offices use both: a pickup group for the team, and BLF keys for reception and managers. If you are also deciding how calls reach the team in the first place, see call queue vs hunt group. Our guide to call pickup groups in Gamma Horizon shows how the group side works.
How do you set up a BLF?
On Horizon, an administrator opens the user in the portal, goes to the Call Setup tab, then Advanced, then Busy Lamp, and chooses which colleagues to monitor. Our Horizon BLF setup guide has the full steps. On a 3CX system the keys are programmed on the handset or in the 3CX management console, and the 3CX desk phone user guide covers day-to-day use.
Frequently asked questions
Is a busy lamp field the same as speed dial?
Not quite. A BLF key does what a speed dial does and also shows the status of the line it points at.
Do softphones support BLF?
Softphone apps usually show colleague presence on screen instead of physical lamps. The idea is the same, but the display is different.
How many BLF keys can I have?
It depends on the phone. On Gamma Horizon the limit is 50 when a sidecar is fitted.
Do cordless handsets support BLF?
It varies by model, so check the handset guide or ask T2K before you buy.
Not sure which handsets suit your team?
Talk to T2K. We will match handsets, keys and call features to how your office actually answers the phone.
Request a quote
