Composite group flashing light

A composite group flashing light is a light whose character is a repeating sequence of groups of flashes with different numbers in successive groups, written for example Fl(2+1). The Fl(2+1) rhythm, two flashes then one, is the standard light of an IALA preferred-channel mark, where the single trailing flash separates it from a plain group-flashing lateral mark. The mariner identifies the light by counting the flashes in each group and reading the pattern against the light list, then takes color and topmark for the full meaning. The composite group distinguishes a junction or modified mark from the ordinary group flashing character it would otherwise resemble.