text: Materials may be used to control and manipulate light via a variety of mechanisms to produce useful effects involving color. For instance, a change of orientation of molecules to produce a visual effect as in liquid crystal displays. Other materials operate by producing a physical effect, by interference and diffraction as in lustre pigments and optically variable pigments, colloidal photonic crystals and in holography. Increasingly inspiration is coming from Nature, in the form of bioinspired structural colors. Molecular materials are also used to increase the intensity of light by modifying its movement through the materials by electrical means, so increasing its intensity as in organic lasers, or in modifying the transmission of light through materials, as in   opto-electronics, or by purely by all optical means as in optical limiters.