Henry IV issued farthings in both the "heavy" (pre 1412) and "light" (1412-13) coinages (20% lighter), although allowing for the prevalence of clipping it is quite difficult to distinguish between the two coinages at the size of the farthing.
Henry V's single issue of farthings (1413-1422) is distinguishable from those of his father because his effigy shows his neck, but is more difficult to distinguish from those of Henry VI's first reign (1422-1461).