Citizen science involves laymen in some steps of a scientific experiment: citizens are volunteers devoting their free time to citizen science projects. Therefore it is important to investigate the factors influencing their motivation and engagement. In this paper, we present our study to investigate the motivation factors of the TESS photometer network participants, an initiative to collect light pollution data. We present the results and insight of our investigation and the instrument we adopted, which can be useful for the broad citizen science community.