To turn off the tap tempo light in a Line 6 Spider V 120 MkII, do the following:
Press and hold the HOME button until setting is displayed.
Rotate the Hold/Save knob clockwise until you see Tap Light.
Press the Hold/Save knob to enter the edit mode.
Rotate the Hold/Save knob to toggle ON/OFF.
Press the Hold/Save knob to confirm.
To exit, do nothing, or press HOME again.