which can be either chemical or physical, that is involved. Many of these phenomena are reversible. The following list includes all the classic chromisms plus many others of increasing interest in newer outlets. There are also chromisms which involve two or more stimuli. Examples include: Photoelectrochromism – Photovoltachromism – Bioelectrochromism – Solvatophotochromism – Thermosolvatochromism – Halosolvatochromism – Electromechanochromism. Color changes are also observed on the interaction of metallic nanoparticles and their attached ligands with another stimulus. Examples include plasmonic solvatochromism, plasmonic ionochromism, plasmonic chronochromism and plasmonic vapochromism. Commercial applications Color change materials have been used in several very common outlets but also in an increasing number of new ones. Commercial applications include photochromics in ophthalmics, fashion/cosmetics, security, sensors, optical memory and optical switches, thermochromics in paints, inks, plastics and textiles as indicators/sensors and in architecture, ionochromics in copy paper, direct thermal printing and textile sensors, electrochromics in car mirrors, smart windows, flexible devices and solar protection, solvatochromics in biological probes and sensors, gasochromics in windows and gas sensors. Dyes and pigments Classical dyes and pigments produce color by the absorption and reflection of light; these are the materials that make a major impact on the color of our daily lives. In 2000, world production of organic dyes was 800,000 tonnes and of organic pigments, 250,000 tonnes and the volume has grown at a steady rate throughout the early years of this century. In 2019 the value of the organic dyes/pigments market is forecast to be $19.5bn. Their value is exceeded by the very large production of inorganic pigments. Organic dyes are used mainly to color textile fibers, paper, hair, leather, while pigments are used largely in inks, paints, plastic and cosmetics. Both are used in the growth area of the digital printing of textiles, paper and other surfaces. Dyes are also made using the properties of chromic substances: Examples being Photochromic dyes and Thermochromic dyes Luminescence The absorption of energy followed by the emission of light is often described by the term luminescence. The exact term used is based on the energy source responsible for the luminescence as in color-change phenomena. Electrical – electroluminescence Galvanoluminescence Sonoluminescence. Photons (light) – Photoluminescence Fluorescence Phosphorescence Biofluorescence. Chemical – Chemiluminescence Bioluminescence Electrochemiluminescence. Thermal – Thermoluminescence Pyroluminescence Candololuminescence. Electron Beam – Cathodoluminescence Anodoluminescence Radioluminescence. Mechanical – Triboluminescence Fractoluminescence Mechanoluminescence Crystalloluminescence Lyoluminescence Elasticoluminescence. Many of these phenomena are widely used in consumer products and other important