The lens body includes a light input portion with a light entry face, a light tunnel extending from the light entry face and defining an optical axis, and a transition face located opposite the light entry face and curved in a plane parallel to the optical axis; a light passage section with a light exit face and coupled to the transition face, such that the transition face is imaged by the light passaged section as a light/dark boundary. An upper surface of the light tunnel defines an ellipsoid with both the maior and minor semiaxes extending in a direction orthogonal to the optical axis; the maior semiaxis being at least 1.9 times the minor semiaxis. A light source might be coupled to the lens body to form a vehicle headlight.