Juniper E Series Hardware Manual page 120

ERX 7.0.x Hardware Guide
Figure 50: SRP Module LEDs
NOTE: The primary SRP module illuminates the REDUNDANT LED only when the
SRP module detects that there is a secondary or standby SRP module online. The
standby SRP module monitors an activity signal from the primary SRP module to
determine its state; it does not shadow the operations of the primary SRP module.
If the standby SRP module detects that the primary SRP module is not active (and
high-availability mode is not enabled), it reboots the system and takes control. If
high-availability mode has been enabled, automatic switchover occurs with near
hitless failover. (ERX-7xx/14xx models only)
104
Understanding Status LEDs to Troubleshoot
Status LEDs
Status LEDs