In a photonic crystal 1, the refractive index of the medium 2, the period of the lattice, and the like are fixed; however, the size of the air holes 3 gradually varies in the direction of the z axis. The stability members may advantageously be placed between outer edge segments of the building surface tiles to restrict relative movement of adjacent surface tiles, such as due to seismic activity, vibrations, or high winds. The recessed area has at least one drain located at a lower area thereof.