(this is suited for space, hence the cigar shape)
there are differently ranked Scourge vessels, light, is a rank. such as the light rank, the dark ran, etc. there are different versions of Scourge dreadnoughts to suit the environment and battle.
A 'light dreadnought' seems pretty contradictory. A dreadnought, by convention, is considerably bigger than a battleship, so 'light' is never really going to be applicable.