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Color and Vision The Electromagnetic and Visible Spectra Electromagnetic waves are waves that are capable of traveling through a vacuum Mechanical waves that require a medium in order to transport their energy, electromagnetic waves are capable of transporting energy through the vacuum of outer space Electromagnetic waves are produced by a vibrating electric charge and as such, they consist of both an electric and a magnetic component Electromagnetic waves exist with an enormous range of frequencies This continuous range of frequencies is known as the electromagnetic spectrum Two very narrow regions within the spectrum are the visible light region and the X-ray region Visible Light Spectrum the very narrow band of wavelengths located to the right of the infrared region and to the left of the ultraviolet region electromagnetic waves exist in a vast range of wavelengths, our eyes are sensitive to only a very narrow band this narrow band of wavelengths is the means by which humans see visible light spectrum This narrow band of visible light is affectionately known as ROYGBIV. Each individual wavelength within the spectrum of visible light wavelengths is representative of a particular color The separation of visible light into its different colors is known as dispersion the colors red (R), orange (O), yellow (Y), green (G), blue (B), and violet (V) visible light - the mix of ROYGBIV - is sometimes referred to as white light Visible Light and the Eye's Response Light that enters the eye through the pupil ultimately strikes the inside surface of the eye known as the retina. The cone sensitivity curve shown above helps us to better understand our response to the light that is incident upon the retina. Since the red cone is sensitive to a range of wavelengths, it is not only activated by wavelengths of red light, but also (to a lesser extent) by wavelengths of orange light, yellow light and even green light. In the same manner, the green cone is most sensitive to wavelengths of light associated with the color green. When a light wave with a single frequency strikes an object, a number of things could happen. The light wave could be absorbed by the object, in which case its energy is converted to heat. The light wave could be reflected by the object. the electrons of atoms have a natural frequency at which they tend to vibrate. When a light wave with that same natural frequency impinges upon an atom, then the electrons of that atom will be set into vibrational motion. (This is merely another example of the resonance principle introduced in Unit 11 of The Physics Classroom Tutorial.) The electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of lihe diagrams depict a sheet of paper being illuminated with white light (ROYGBIV). The papers are impregnated with a chemical capable of absorbing one or more of the colors of white light. Such chemicals that are capable of selectively absorbing one or more frequency of white light are known as pigments get are said to be reflected Transparent materials are materials that allow one or more of the frequencies of visible light to be transmitted through them; whatever color(s) is/are not transmitted by such objects, are typically absorbed by them. The appearance of a transparent object is dependent upon what color(s) of light is/are incident upon the object and what color(s) of lig ht is/are transmitted through the object. Color perception, like sound perception, is a complex subject involving the disciplines of psychology, physiology, biology, chemistry and physics. When you look at an object and perceive a distinct color, you are not necessarily seeing a single frequency of light. . Any three colors (or frequencies) of light that produce white light when combined with the correct intensity are called primary colors of light. The graphic at the right is extremely helpful in identifying complementary colors. Complementary colors are always each other on the graphic located directly across from Color Subtraction Specific pigments will selectively absorb specific frequencies of light in order to produce a desired appearance. W - B = (R + G + B) - B = R + G = Y C - B = (G + B) - B = G the misconception that was targeted earlier in Lesson 2 as we discussed how visible light interacts with matter to produce color. In that part of Lesson 2, it was emphasized that the color of an object does not reside in the object itself While most pigments absorb more than a single frequency (and are known as compound pigments), it becomes convenient for our discussion to keep it simple by assuming that a yellow pigment absorbs a single frequency. A pigment that absorbs a single frequency is known as a pure pigment. Pigments absorb light. Pure pigments absorb a single frequency or color of light. The color of light absorbed by a pigment is merely the complementary color of that pigment. Primary Colors of Paint A trip to the local newspaper or film developing company will reveal these same principles of color subtraction at work. The three primary colors of paint used by an artist, color printer or film developer are cyan (C), magenta (M), and yellow (Y). Artists, printers, and film developers do not deal directly with light; rather, they must apply paints or dyes to a white sheet of paper. These paints and dyes must be capable of absorbing the appropriate components of white light in order to produce the desired affect. Most artists start with a white canvas and apply paints. These paints have to subtract colors so that you might see the desired image. An artist can create any color by using varying amounts of these three primary colors of paint. Magenta paints absorb green light. Cyan paints absorb red light. Yellow paints absorb blue light Blue Skies and Red Sunsets