Optic for a LED chip, in particular of COB type, including a second element realized with an optical transparent material and having a first proximal end and a second distal end, a second external exit surface, a first total internal reflection external lateral surface which redirects and re-distributes a luminous flux realized by LED chip towards the second external exit surface, the second element including an internal blind cavity for housing LED chip. The optic includes a disc shaped first element extending externally with respect to said second element in an orthogonal direction to a longitudinal direction, and the first element and the second element are mutually integral through injection molding, and realized in one single piece through injection molding using optic grade transparent silicone elastomer for making a LED lighting device waterproof and anti-shock, avoiding the need of a gasket and external glass, and with reduced components.