In ScreenOS you can get the alarm event that created the red or yellow alert via the cli. You will need to fix the alarm condition for the light to go out.
get alarm event
If the alarm is from a security attack event that is no longer in progress you can clear the led.
clear led alarm
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Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
http://puluka.com/home------------------------------