A smart window includes two transparent substrates and a liquid crystal layer. The two transparent substrates are opposite to each other and are electrically connected to a voltage supply. A first pulse voltage or a second pulse voltage is provided between the two transparent substrates by the voltage supply. The liquid crystal layer is located between the two transparent substrates and has a liquid crystal material. The liquid crystal material has a pitch of at most 250 nanometers or at least 500 nanometers. The liquid crystal material includes a nematic liquid crystal, a rotatory molecule, and a photochromic dye mixed with each other. The liquid crystal material changes a transmittance corresponding to a specific light wavelength range when receiving a light. The liquid crystal material is switched between a planar texture and a focal-conic texture respectively according to the first pulse voltage and the second pulse voltage.