In the Fall of 2018, the first in a pair of full-scale prototypes of the Deep Underground Neutrino Experiment (DUNE) Far Detector known as ProtoDUNE- Single Phase (SP), was activated. ProtoDUNE-SP consists of a Liquid Argon Time-Projection Chamber (LArTPC), integrated Photon Detection System (PDS) and Cosmic-Ray Tagger (CRT) configured to observe particles provided by the CERN SPS, however cosmic-ray events are also present. This poster presents an analysis of the light produced by cosmic-ray muons identified using the CRT and TPC. The relationship between the observed light in an S-ARAPUCA PDS module versus the distance to the track was compared between data and simulation and agreed better with a Rayleigh scattering length of 90 cm rather than 60 cm.