A light trail refers to a visible path of non-dangerous, solid-looking light that some emitters would create in the air. Typically, nearly all Blastswords produced light trails, in addition to some lightsabers and other energy-based equipment when they were either designed to do so, or moved quickly enough.
New Republic pilot Wes Janson, who developed an affinity for the weapon during a diplomatic trip to Adumar, often used Blastsword light trails for comedic effect.