In LED luminaires, what determines the life of the light source is not current but temperature. The body has to take the heat produced by the driver and the module and give it to the outside; a luminaire that cannot do this never reaches its catalogue life.
The cast body brings heat sink fins, the optic seat, the gasket groove and mounting lugs together in one piece. Street and tunnel luminaires add outdoor durability: the geometry is laid out so water cannot pool and fins do not trap dust.
Surface treatment is chosen for both corrosion resistance and emissivity — a dark, matte surface radiates heat better than a bright one.