Physics
Spectral Colour
Spectral color refers to the specific colors that make up the visible light spectrum, which includes red, orange, yellow, green, blue, indigo, and violet. Each of these colors corresponds to a specific wavelength of light. When combined, these spectral colors create white light. Spectral colors are fundamental to understanding the behavior of light and its interaction with matter.
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10 Key excerpts on "Spectral Colour"
eBook - PDFColour and the Optical Properties of Materials
An Exploration of the Relationship Between Light, the Optical Properties of Materials and Colour
- Richard J. D. Tilley(Author)
- 2010(Publication Date)
- Wiley(Publisher)
(a) The colours of the spectrum are arranged around a curved line and nonSpectral Colours fall on the line joining violet (400 nm) and red (700 nm). The figures marked around the outer edge of the curve denote the wavelength of the colour. Points within the area of the diagram represent colours formed by the additive mixing of light and can be specified by the appropriate x-and y-values. The point W represents white light. (b) A straight line through W links two complementary colours on the periphery of the diagram, in this example red and cyan. (c) The lever rule gives the proportions of complementary colours which are needed to create white light. In this example, the amount of red light is given by r/(r þ c) and the amount of cyan light by c/(r þ c) Colour and the Optical Properties of Materials 32 1.13 The Interaction of Light with a Material Colour is inherent in the light that leaves an emitting source; but most often before it reaches the eye it interacts with matter of many types: gases, liquids and solids. The colour observed is thus a function of both the source radiation and the interactions that have occurred. The way that light interacts with a material can be described in terms of scattering or absorption. To a first approximation, scattering is well treated by assuming that the light behaves as an electromagnetic wave, while absorption is best treated in terms of photons. If the energy of the scattered wave/photon is the same as that of the incident wave/photon then the scattering is called elastic scattering, and otherwise inelastic scattering. For historical reasons, the term scattering itself, especially elastic scattering, is usually reserved for the interaction of light with randomly distributed small particles. Elastic scattering from a surface is normally called reflection , and elastic scattering into a transparent solid is called refraction .
- Rangayyan, Rangaraj M., Acha, Begoña, Serrano, Carmen(Authors)
- 2011(Publication Date)
1 The Nature and Representation of Color Images Color is an important and often pleasant part of the visual domain; however, color is not a physical quantity but a human sensation. Color is the visual perception generated in the brain in response to the incidence of light, with a particular spectral distribution of power, on the retina. The retina is com-posed of photoreceptors sensitive to the visible range of the electromagnetic (EM) spectrum [21,36–38]. In general, different spectral distributions of power produce distinct responses in the photoreceptors, and therefore, different color sensations in the brain. See Table 1.1 for a representation of the EM spectrum and its parts related to various modalities of imaging, and Figure 1.1 for a display of the visible color spectrum as a part of the EM spectrum [1,39]. The diffraction of sunlight by water shows the visible color spectrum in the form of a rainbow; see Figure 1.2 for an example. When a surface is illuminated with a source of light, it absorbs some parts of the incident energy and reflects the remaining parts. When a surface is identi-fied with a particular color, for example, red, it means that the surface reflects light energy in the particular range of the visible spectrum associated with the sensation of red and absorbs the rest of the incident energy. Therefore, the color of an object varies with the illumination. An object that reflects a part of the light that is incident upon it may be considered a secondary source of light. To reproduce and describe a color, a color representation model or color space is needed. Many color spaces have been proposed and designed so as to Figure 1.1 The visible color spectrum and approximate naming of its constituent colors.
- Derek H. Brown, Fiona Macpherson, Derek H. Brown, Fiona Macpherson(Authors)
- 2020(Publication Date)
- Routledge(Publisher)
124 The science of colour and colour vision The refectance of an object (or surface) at a given wavelength is the ratio of the light (number of photons) it reflects at that wavelength to the incident light at that wavelength. The surface spectral refectance (SSR) of an object is the reflectance of the object at each wavelength (in prac-tice narrow bands of wavelengths) in the visible spectrum. Displaying an object’s SSR graphi-cally results in its spectral refectance curve . In order to achieve a widespread system of colour measurement the illuminants need to be standardized. The most important of these is CIE illu-minant C —an approximation to average daylight that has the virtue of being reproducible in the laboratory using a standard light source and filter. The visible light reaching the eye from an (opaque, non-luminous) object is the joint product of its SSR and the SPD of the incident light. Ignoring the effects of scene composition, these exhaust the physical characteristics of objects and light relevant to predicting colour appearance. 2 What is missing, however, from this physical description is any way of relating this information to perceived colour. First, not all differences in the SSR of the object or the SPD of the illumi-nant are perceptually detectable. Second, and more importantly, a pair of spectral reflectance curves is little help by itself as to whether or not the corresponding two objects will appear to match in colour when viewed in a given illuminant. Unsurprisingly, the physics of light and its interaction with objects is not enough to explain how we perceive colour. 4 Basic physiology of colour vision Perceived colour is, in complicated ways, dependent on the spectral power distribution of the light reaching the eye from the objects in the scene. This entails that there are mechanisms in the eye/brain that respond differentially to light of different wavelengths.
eBook - ePubColour Reproduction in Electronic Imaging Systems
Photography, Television, Cinematography
- Michael S. Tooms(Author)
- 2015(Publication Date)
- Wiley(Publisher)
We are now getting into the detail of what colours we see when certain parts of the spectrum are missing. We know that when the eye is exposed to a spectrum comprising broadly equal amounts of light from violet to red, we perceive the colour white; but in order to be able to predict what we see when a combination of elements of the spectrum are present, we need to investigate how the eye–brain complex responds to mixtures of elements of the spectrum. To do this we need to characterise in some detail how the eye responds to light of differing levels and to light of various frequencies or wavelengths within the spectrum.1.3 Characterising the Responses of the Eye to Light
Colour is the term we use to describe how the eye perceives light of varying strength at different wavelengths, and light may be defined as the energy in that segment of the electromagnetic spectrum to which the eye responds. The electromagnetic spectrum in its entirety is extremely broad and comprises with increasing frequency: radio, infrared, light, ultraviolet, x-rays and gamma rays. In many branches of science and engineering electromagnetic energy is discussed in terms of frequency whilst in others it is in terms of wavelength. Wavelength and frequency of light are inversely related by the speed of light such that the wavelength ‘λ’ (lambda) equals the speed of light ‘c’ divided by the frequency ‘f’ in cycles per second.2where c = 2.99792458 × 108 m/s or very nearly 3 × 108 m/s.In treating the subject of light and colour the general practice is to refer to light of a given wavelength rather than to its frequency and to a band of wavelengths as a spectrum.The eye perceives colour as a characteristic of light. Light is formally that very narrow segment of the electromagnetic energy spectrum occupying wavelengths of approximately 380–720 nm. (A nanometre or nm is one thousand millionth of a metre or 10−9
eBook - PDFComputer Graphics
Theory and Practice
- Jonas Gomes, Luiz Velho, Mario Costa Sousa(Authors)
- 2012(Publication Date)
- A K Peters/CRC Press(Publisher)
5 Color Color plays an important role in the study of images, and more generally in computer graphics. It will therefore occupy us for more than one chapter. Here we start to approach the subject by asking, What is color? What are the mathematical models for color? How should colors be discretized? As usual, our approach will be based on the four universes paradigm, as follows: Colors in Phys. Universe −→ Mathematical Models −→ Color Representation −→ Color Specification 5.1 Color in the Physical Universe Color arises from electromagnetic radiation within a range of wavelengths that affect the human eye. The visible electromagnetic spectrum lies between the wavelengths of Gamma rays X-rays Ultra- violet Infrared microwaves Radio waves Visible light Wavelength (nm) 400 500 600 700 Figure 5.1. Electromagnetic spectrum; top diagram has a logarithmic scale. (See Color Plate I.) 109 110 5. Color (a) (b) Figure 5.2. (a) Spectral distribution of sunlight and (b) of some standard illuminants. λ a = 400 nm and λ b = 800 nm, approximately (the nanometer, abbreviated nm, is one billionth of a meter). Figure 5.1 shows the visible spectrum as a part of the much broader spectrum of all electromagnetic radiation, most of which is not visible. The energy associ- ated with an electromagnetic wave is called radiant energy. Color is a psychophysical phenomenon, that is, it has an important perceptual compo- nent, in addition to its physical aspects. There are three important areas in the study of color: colorimetry, radiometry, and photometry. Colorimetry deals with the representation and specification of color, ignoring its physical nature and propagation properties. Ra- diometry deals with physical measures associated with radiant energy, while photometry deals with perceptual measurements of radiant energy as illumination. In this chapter we discuss colorimetry; the other two areas are briefly covered in Chapter 18.
eBook - ePubChromic Materials
Fundamentals, Measurements, and Applications
- Michal Vik, Aravin Prince Periyasamy, Martina Viková(Authors)
- 2018(Publication Date)
- Apple Academic Press(Publisher)
Figure 1.2 ).Similarly, in other cases like the electromagnetic spectrum, it is impossible to define exact borders. The entire range of wavelength is divided in Table 1.1 , which represents spectral colors and approximate wavelength intervals associated with them.1.2 Blackbody RadiationThe temperature of a blackbody radiator can be used as a means to quantify the energy distribution of an illuminant. If a metallic object is heated, after a short time, it becomes too hot to touch. This is due to emission of infrared radiation. With more heating, the object begins to glow; first, a dull red color appears, followed by bright red, yellow, white, and even blue at higher temperatures. Blackbody radiation or cavity radiation refers to an object or system that absorbs all radiation incident upon it and re-radiates energy; this characteristic of the radiating system does not dependent upon the type of radiation which is incident upon it. The radiated energy can be considered to be produced by a standing wave or resonant modes of the cavity, which is radiating (Figure 1.3 ).FIGURE 1.2 The electromagnetic spectrum.Classical description of blackbody radiation is based on Rayleigh-Jeans law:TABLE 1.1 Color of Absorbed Light and Corresponding Complementary Colors(1.4)E=v0k T2 πv 2c 2where k = 1.380662×10−23 J.K−1 is Boltzmann constant, and T is thermodynamic temperature in kelvins (K).FIGURE 1.3
Available until 3 Feb |Learn moreLighting for Driving
Roads, Vehicles, Signs, and Signals
- Peter R. Boyce(Author)
- 2008(Publication Date)
- CRC Press(Publisher)
Exactly what colour will be seen depends not only on the spectral distribution of the radiation incident on the retina but also on such factors as the luminance and colour of the surroundings and the state of adaptation of the observer (Purves and Beau Lotto 2003). Colour is a perception developed in the brain from past experience and the information contained in the retinal image. Light itself is not coloured. Nonetheless, to have a means of character-izing the colour perception associated with different light sources and other stimuli to the visual system, some way had to be found to provide quantitative measures of colour. The CIE colourimetry system provides such measures. 2.4.1 T HE CIE C OLOURIMETRY S YSTEM The basis of the CIE colourimetry system is colour matching, an activity in which an observer is asked to determine whether two fields are the same or different in colour. From extensive colour matching measurements, the CIE Colour Matching Functions have been determined. These functions are essentially the relative spectral sensitivity curves of human observers with normal colour vision and can be considered as another form of standard observer. There are three colour matching functions, as might be expected from the fact that humans with normal colour vision can match any colour of light with a combination of not more than three wavelengths of light from the long, medium, and short wavelength regions of the visible electromagnetic spectrum. The colour of a light source can be represented mathematically by multiplying the spectral power distribution of the light source, wavelength by wavelength, by each of the three colour matching functions x( λ ), y( λ ), and z( λ ), the outcome being the amounts of three imaginary primary colours X, Y, and Z required to match the light source colour.
eBook - PDF- Andrew Fraknoi, David Morrison, Sidney C. Wolff(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
Light is one form of this electromagnetic radiation. The wavelength of light determines the color of visible radiation. Wavelength (λ) is related to frequency (f) and the speed of light (c) by the equation c = λf. Electromagnetic radiation sometimes behaves like waves, but at other times, it behaves as if it were a particle—a little packet of energy, called a photon. The apparent brightness of a source of electromagnetic energy decreases with increasing distance from that source in proportion to the square of the distance—a relationship known as the inverse square law. 5.2 The Electromagnetic Spectrum The electromagnetic spectrum consists of gamma rays, X-rays, ultraviolet radiation, visible light, infrared, and radio radiation. Many of these wavelengths cannot penetrate the layers of Earth’s atmosphere and must be observed from space, whereas others—such as visible light, FM radio and TV—can penetrate to Earth’s surface. The emission of electromagnetic radiation is intimately connected to the temperature of the source. The higher the temperature of an idealized emitter of electromagnetic radiation, the shorter is the wavelength at which the maximum amount of radiation is emitted. The mathematical equation describing this relationship is known as Wien’s law: λ max = (3 × 10 6 )/T. The total power emitted per square meter increases with increasing temperature. The relationship between emitted energy flux and temperature is known as the Stefan-Boltzmann law: F = σT 4 . 182 Chapter 5 Radiation and Spectra This OpenStax book is available for free at http://cnx.org/content/col11992/1.13 5.3 Spectroscopy in Astronomy A spectrometer is a device that forms a spectrum, often utilizing the phenomenon of dispersion. The light from an astronomical source can consist of a continuous spectrum, an emission (bright line) spectrum, or an absorption (dark line) spectrum.
eBook - PDFArt in Chemistry
Chemistry in Art
- Barbara R. Greenberg, Dianne Patterson(Authors)
- 2007(Publication Date)
- Libraries Unlimited(Publisher)
4. Discuss the subject of your picture. What is the chemistry significance of your subject matter? LIGHT AS A SOURCE OF COLOR: THE ELECTROMAGNETIC SPECTRUM How are light and color related? • Visible white light is a source of color. The color observed for an object is a function of the light source and the reflective and absorbing properties of the surface that the light strikes. • If white light strikes a red apple, because white light contains all of the visible colors—red, orange, yellow, green, blue, indigo, and violet, all of the visible colors will be absorbed except for red, which will be reflected. Thus, the apple is red. Color begins with and is derived from light, either natural or artificial. Where there is little light, there is little color; where the light is strong, the color is likely to be particularly intense. We notice at such times as dusk or dawn, when the light is weak, that it is difficult Light as a Source of Color: The Electromagnetic Spectrum / 9 to distinguish one color from another. Under bright, strong sunlight, such as in tropical climates, colors have more intensity. Where does all light come from? • Initially, all light comes to us from the sun. • Certain atoms and molecules store light energy and emit that light energy under certain conditions, such as during a chemical change. Burning is a common example of such a chemical change. • Light from atoms also appears when excited atoms release energy. What is electromagnetic radiation? • A form of energy that travels in waves is called electromagnetic radiation. • The following relationship exists between the wave frequency, n, and wavelength, l: frequency times wavelength = velocity. Velocity refers to the speed of electromagnetic radiation waves in a vacuum. It is a constant (2.998 x 10 8 m/s), sometimes called the speed of light, c.
eBook - PDFFood Colorants
Chemical and Functional Properties
- Carmen Socaciu(Author)
- 2007(Publication Date)
- CRC Press(Publisher)
An impressive example is the throat of the purple-throated mountain gem ( Lampornis calolaema ), whose reflected color depends strongly on the angle under which it is observed. 1 Another spectral light modulation occurs in the case of fluorescent matter. When an object is illuminated by ultraviolet (UV) light, a bright fluorescence emission in the visible spectral region may appear. This has impressively been dem-onstrated with another bird, the budgie ( Melopsittacus undulatus ), under different light conditions. 1 The same properties hold for colorants in food: interference colors, illumination conditions, and fluorescence partially determine the appearance of food. The laws of geometrical optics strongly determine the appearance of food and food colorants, depending in detail on the transparency of the matter and how homogeneous it is. The spectral variations caused by the interference phenomena become relevant when a food contains tightly adjoining dense structures like feathers, fish scales, or the shells of crustaceans. Natural food and food colorants show weak or no fluorescence. But food may be incorporated easily by fluorescing pigments that impart bright colors to the matter when it is irradiated by blue or UV light, where usually fluorophores are excited to emit light in the visible region. Comparing food colors under daylight and under UV light helps to identify artificial color additions. 1.3 PHYSICAL NATURE OF LIGHT AND COLOR About 100 years ago, Albert Einstein established the modern understanding of light and color. Based on it, up to now, tremendous development of optical technologies including laser technology and color analysis methods has taken place. Also, the interaction of light with biological matter evolved since then from an empirical description to a basic understanding. The interaction of light with inorganic and organic matter follows the same laws. Basic biologic processes like photosynthesis and vision are fairly well under-stood.
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