Abstract: An electrically controlled medium for modulating light includes two plastic thin film layers (1) and (2), and a mixture layer (3) is arranged between the two plastic thin film layers (1) and (2). The mixture layer (3) is consisted of smectic liquid crystals (31), polymer materials (33) and dopants (32). Electrode layers (4) are coated on one side of each of the two plastic thin film layers (1) and (2) facing to the mixture layer (3), and the electrode layers (4) are connected to a device of electrical driving system (5). The liquid crystal molecules are allowed to exhibit different molecule alignments by controlling the amplitude, frequency and driving time of the electric power applied to the electrode layers (4), so that the electrically controlled medium for modulating light can be switched between a blurredly scattering state and a fully transparent state, even may be switched among a plurality of gradual translucent states of different gray levels.