Light is one of the interesting concepts used for explaining the important processes in modern physics. Because of this reason the students have some misunderstandings and difficulties about light and related phenomena. The present study aims to determine pre-service teachers' understanding of and difficulties with light concept via mental models of light utilized by the students for the explanations of Compton Effect. This research has been carried on the group of 25 students studying in the departments of physics education at a Government University in Turkey. As a data collection tool open - ended questions pertaining drawings and explanations were used. The participants consist of 15 female and 10 male students and they ranged from 22 to 24 years of age. According to the results of this study three mental models which were named as hybrid model, ray and particle model were determined used by the students while explaining the Compton Effect. Implications of our findings for teaching are discussed. (C) 2015 The Authors. Published by Elsevier Ltd.