A method includes: preparing a substrate having a plurality of light sources on a front side, a case to be provided on a back side of the substrate, the case having a side wall along a periphery of the case, and a mask having a light shielding member and a side wall projecting to the back side at a periphery of the mask, the light shielding member having a plurality of windows for transmitting light from the plurality of light sources, an outer shape of the mask being larger than an outer shape of the substrate and an outer shape of the case when viewed from the front side; fixing the case, the substrate, and the mask; filling a fluid material between a side wall of the case and a side wall of the light shielding member; and hardening the fluid material.