This study is a qualitative study carried out to compare the effectiveness of concept cartoons and open-ended questions to determine the alternative ideas of pre-service science teachers about “light”. The participants of the study, which was conducted in Ataturk university Education Faculty, were 212 pre-service science teachers who are in the 1st , 2nd , and 3rd grades. The alternative ideas of pre-service science teachers were investigated by using concept cartoons and open-ended questions. Two tests made of concept cartoons and open-ended questions were used to determine the alternative ideas of the pre-service science teachers in the study. The data of the study was analysed using content analysis. It was found that the pre-service science teachers possessed some alternative concepts such as white cat could be seen in darkness and stars can not be seen in daylight because they only reflect moon light and while determining these alternative ideas, concepts cartoons were as effective as open-ended questions.It was found that pre-service science teachers had some alternative ideas and concept cartoons were as suitable as the open-ended questions to determine these alternative ideas. Preservice science teachers have ideas white cat can be seen in the dark, the stars can’t be seen only in the light of the day to reflect the moonlight.