A method of fabricating a light duct includes making the light duct as a single piece by injection molding a thermoplastic material in a mold (1) presenting a cavity of shape identical to that of the duct, the injection taking place through a feed orifice disposed on one side of said cavity over a face that is substantially parallel to the plane defined by axes (A-A′, B-B′), the feed orifice presenting a height h lying in the range 0.2 Hmax and Hmax, and a length l lying in the range 0.2 Lmoy and 0.8 Lmoy, the thermoplastic material being injected at a rate lying in the range 400 mm3/s to 1500 mm3/s.