Purple exists only in our brains

Summary

acronym: A word made by combining some of the starting letter or groups of letters from a number of words. For instance, STEM is an acronym for Science, Technology, Engineering and Math. Radar is an acronym for RAdio Detection And Ranging. Even laser is an acronym for Light Amplification by Stimulated Emission of Radiation. activate: (in biology) To turn on, as with a gene or chemical reaction. cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. cones: (in biology) A type of eye cell that is part of the retina inside the back of the eye. These cells can sense red, green or blue light. Recent research has uncovered evidence that many can sense white light — but only white light. electromagnetic: An adjective referring to light radiation, to magnetism or to both. electromagnetic radiation: Energy that travels as a wave, including forms of light. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light. electromagnetic spectrum: The range of radiation that spans from gamma- and X-rays through visible light and on to radio waves. Each type of radiation within the spectrum typically is classified by its wavelength. gradient: From the word “grade,” it describes the incline, slope or degree of increase in some measure (such as temperature, pressure or even color) that develops as one moves in time, position or along some scale. microwaves: An electromagnetic wave with a wavelength shorter than that of normal radio waves but longer than those of infrared radiation (heat) and of visible light. nanometer: A billionth of a meter. It’s such a small unit that researchers use it as a yardstick for measuring wavelengths of light or distances within molecules. For perspective, an average human hair is about ...