Optic for a LED chip and related LED lighting device

An optic for a LED chip (97) of the COB type, said optic comprises a second element (50) realized with an optical transparent material and having a first proximal end (51) and a second distal end (53), a second external exit surface (58) which is positioned in proximity of said second distal end (53), a first external lateral total internal reflection surface (59) which is positioned between said first proximal end (51) and said second distal end (53) and which is able to redirect and re-distribute a luminous flux produced by said LED chip (97) towards said second external exit surface (58), further said second element (50) comprises a blind internal cavity (52) realized in proximity of said first proximal end (51), which extends internally to said second element (50) substantially along a longitudinal direction (90) towards said second external exit surface (58) for housing said LED chip (97), characterized in that said optic comprises a first element (30) substantially disc shaped, having a central hole (32), which extends externally with respect to said second element (50) in an orthogonal direction with respect to said longitudinal direction (90), and in addition said first element (30) and said second element (50) are formed as a single unitary whole, furthermore said first element (30) is compressible independently with respect to said second element (50) for making said LED chip (97) waterproof and also an electronic board (95) by avoiding at the same time an undesirable modification in the optical properties of said second element (50) and by avoiding at the same time the need of a gasket.