According to the method for controlling optical transmissions according to the present invention, in a state where particles formed of a light-blocking material, a first solvent with electro-wetting properties in which the particles are dispersed, and a second solvent which is not mixed with the first solvent are present in a space covered by an optical incident surface, the particles are mixed with the first solvent but not mixed with the second solvent, and an electric field applied to the first solvent is controlled so as to control the blocking area of the first solvent with respect to the optical incident surface and control optical transmittance.