The Rotating Drum Spectrometer (RDS) experiment is planned to be placed onboard Ruscosmos Multipurpose Laboratory Module ”NAUKA” on the International Space Station (ISS) in 2019. The experiment is designed to measure X-ray spectra of Solar flares using Bragg reflection from flat crystals. Additionally to the reflection of X-ray photons crystals produce luminescent light. In order to separate those physical effects during real experiment data analysis, computer simulations are necessary. Using Geant4 toolkit we simulated particle background, which were generated by several processes: photoelectric effect, Compton scattering and Bremsstrahhlung. In this paper we present luminescent light background estimations in the RDS instrument.