thumb|Trilux Small Arms Sight Unit
thumb|upright=1.35|Sight attached to an [[L85A2]]
The Sight Unit Small Arms, Trilux, or SUSAT, is a 4× telescopic sight, with tritium-powered illumination utilised at dusk or dawn. The full name of the current model is the SUSAT L9A1. The sight is not designed as a sniper sight, but is rather intended to be mounted on a variety of rifles and to be used by all infantrymen.
Similar devices include the Advanced Combat Optical Gunsight (ACOG), manufactured by Trijicon, and the Elcan Specter.
Use
<!--thumb|right|An L85A1 field stripped with SUSAT. Removed image hidden-->
SUSAT was the primary sighting system for the British Army's SA80 series weapons.