The room-temperature reflectivity of single-crystal Ba2NaNb 5O15 has been measured in the range from 10 000 to 70 cm-1. Separate measurements were taken for the electric field of the light polarized parallel to the c axis and perpendicular to the c axis. The data were analyzed by using the Kramers-Kronig relations and also by fitting the reflectivity spectrum to a classical independent oscillator dispersion model. The results are compared to previous Raman and infrared measurements. The linewidths obtained from the infrared measurements are found to be considerably broader than the Raman linewidths. © 1972 The American Institute of Physics.