On the basis of lead tiogalat (PbGa2S4) was created the active elements for lasers which allow to control the generation spectroscopic properties of lasers and parameters of the laser radiation [1]. In these crystals were found Frenkel excitons with large oscillator strength (292meV) at room temperature. At a temperature of 10 K was observed the Wannier-Mott exciton [2]. The contours of the exciton reflection spectra of Frenkel and Wannier-Mott excitons, for PbGa2S4 crystals, was calculated on the basis of dispersion relations [3], Figure 1. It allow to determine the value of the splitting due to crystal field (Δкр), spin-orbit (Δso)interaction of the upper valence bands in the center of the Brillouin zone in PbGa2S4 crystals. At the minimum of interband gap the exciton series A is formed by pair of bands (V1-C1) with Г Г 5 5 − ± symmetry, the B series is formed by pair of zones (V2-C2) with Г Г 5 5 − ± symmetry. In this model, both exciton series is formed in the center of the Brillouin zone, at same value of the wave vector 0 k  . Zones C1 and C2 are degenerate in the center of the Brillouin zone. The values of band gap for the polarizations Е⊥ c and Е||с, obtained from calculations of the exciton spectra coincede.In the energy range 3-6eV was measured reflection spectra at temperatures of 14, 77 and 300 K for the polarization E ⊥c with E ||c. The experimental spectra are calculated by the Kramers-Kronig relations and determined the optical constants n, k, ε1 and ε2. The observed transitions for PbGa2S4 crystals, is discussed in the theoretical calculations of the energy band structure of tiogalat crystals. On the basis of PbGa2S4 possible to predict the creation of optoelectronic devices, operating at room temperature, the action is based on physical principles of interaction of light with excitons.figureFig.1. Experimental and calculated contours of reflection spectra of Wannier-Mott (A-eks.) and Frenkel (B-eks.) excitons in PbGa2S4 crystals