The chassis beacon feature helps identify a specific Juniper device or port by slowing the port status LED to a steady green blink, making it easier for onsite personnel to locate the device or port.

By default, when a network port and its associated link are active, the status LED for that port blinks green at a rate of 8 blinks per second. With the chassis beacon feature, you can use the request chassis beacon command to slow the current rate at which the status LED blinks green to 2 blinks per second. The slower and steadier green light acts as a beacon that you, as a network administrator in a remote office, can enable to guide a network installer in a busy data center or lab to a Juniper Networks device or port on the device. 

You can use the following options with the chassis beacon feature:

• Turn on the beacon for:

  • 5 minutes (default)

  • A specified number of minutes (1 through 120)

• Turn off the beacon:

  • Immediately

  • After a specified number of minutes (1 through 120) elapses

You can use these options on all network ports on an FPC or just one network port on an FPC.

To turn the beacon on or off on a Virtual Chassis, you must:

• Issue the request chassis beacon command on the primary switch in the Virtual Chassis.

• When specifying the FPC slot number, use the target Virtual Chassis member number.

https://www.juniper.net/documentation/us/en/software/junos/system-mgmt-monitoring/topics/task/chassis-beacon-light.html