An experiment useful to investigate crystallinity evolution during fast cooling, comparable with cooling rates attained in industrial processes, is extremely attractive. In this work, a setup able to quench thin polymer films while recording the sample thermal history and light intensity of a laser beam transmitted by the sample is described. A particular feature of the optical measurement setup is the use of a LED array as receiver enabling to monitor as well changes in the polarization properties as changes in light scattering of the polymer during crystallization. Furthermore it could be demonstrated that the LED array can be used as a linear optical detector with photocurrent gain values exceeding 10 when polarized slightly below reverse bias breakdown.