2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/162213In this paper we prove several multiplicity results of $t$-periodic light rays in conformally stationary spacetimes using the Fermat metric and the extensions of the classical theorems of Gromoll-Meyer and Bangert-Hingston to Finsler manifolds. Moreover, we exhibit some stationary spacetimes with a finite number of $t$-periodic light rays and compute a lower bound for the period of the light rays when the flag curvature of the Fermat metric is $η$-pinched.15 pages. Lemma 2.1 modified due to an incorrect statementDifferential Geometry53C22, 53C50, 53C60, 58B20text