Lucent Technologies PARTNER Advanced Communications System Programming And Use Instructions page 71

Lights
Each line or pool button has a green light and a red light. The meaning of these
lights varies, depending on whether the button is used to access an outside line or
pool, is programmed with a system feature, or is programmed for Auto Dialing an
extension number (Intercom Auto Dial button). (Auto Dial buttons for fax
extensions show additional information; these "Fax Management" buttons are
described in
information about programmed settings; see
Table 3-1 shows the meanings of the various light patterns for each possible
button assignment.
3-4
Learning About Telephones
Chapter 4. When a phone is in programming mode, the lights show
Chapter 2 for details.)