Let V−>B be a holomorphic family of smooth complex projective and polarized varieties. The Noether-Lefschetz locus of B is the set of points x where the Picard rank jumps, i.e. where H_2(V_x) has exceptional integral classes of type (1,1). I will explain that, when B has the correct dimension, the Noether-Lefschetz locus "equidistributes" toward a smooth volume form given by a characteristic class of the Hodge bundle. The proof uses homogeneous dynamics and reduces to a study of the invariant cohomology of period domains. This is a joint work with Salim Tayou.