Provided are a light modulation device and a use thereof. The light modulation device may apply an external signal by a composite layer having a high transmittance in a visible region, a low transmittance in an infrared region and a low sheet resistance. Such a light modulation device may be applied in various uses such as a smart window, a window protecting film, a flexible display element, an active retarder for displaying a 3D image or a viewing angle control film.