In this work, we demonstrated a smart window application that could control white light diffraction based on electrohydrodynamic instability. The device could switch between the transparent and diffraction states via an applied voltage. We investigated the diffraction properties of the active anti-glare device. The results indicated that the device could be controlled via a change of the focal length between positive and negative values, with a negative focal length causing white light diffraction. The proposed device has promise for use as a smart window that can be controlled via an applied voltage.