Panasonic KX-TD500 System Reference Manual page 391

3.00 LED Indication Patterns
Line conditions are displayed by three patterns of flashing LED indicators on PITS buttons, as follows.
Pattern 1
(240 wink)
Pattern 2
(60 wink)
Pattern 3
(120 wink)
1 sec
Pattern 1 : Shows call arriving with 240 winks/min and is called "240 wink".
Pattern 2 : Shows holding a call with 60 winks/min and is called "60 wink".
Pattern 3 : Shows Unattended Conference and Privacy Release with 120 winks/min and is called "120
wink".
Light on steady shows busy status and light off shows idle status.
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