Must be the cold in my head that's causing me to make things too complicated...

Code:
If daycount = 0 THEN
   If Counter1 = sumplighton Then
     high sump_light
     daycount = 1
  ENDIF
ENDIF

IF daycount = 1 THEN
  If Counter1 = sumplightoff Then
    low sump_light
    daycount = 0
  ENDIF
ENDIF
based on your example I came up with the above which works just fine !

Thanks Henrik