The non - accelerator observation of the long - range strong nuclear interaction is presented. We have studied the low - temperature spectra (reflection and luminescence) of the LiH (without strong interaction in hydrogen nucleus) and LiD (with strong interaction in deuterium nucleus) crystals which are different by term of one neutron from each other. The experimental observation of isotopic shift (103 meV) of the phononless free excitons emission line in LiD crystals is a direct manifestation of the long - range strong nuclear interaction. Such conclusion is made to the fact that the gravitation, electromagnetic and weak interactions are the same in both kind crystals, it only emerges the strong interaction in deuterium nucleus. As far as Born - Oppenheimer approximation does not work in isotope effect, we tentative connect our experimental observation with long - range hadron - lepton interaction. Most important study of the LiHx D1-x mixed crystals is the first measurement of the long - range force dependence of strong nuclear interaction on the distance between nucleons in deuterium nucleus