Colorimetry defined

Colorimetry [1.17] - [1.19]. The principles of colorimetry are based on the fact that all color stimuli can be simulated by additively mixing only three selected color stimuli (trichromatic principle). A color stimulus can, however, also be produced by mixing the spectral colors. Thus, it has a spectral distribution, which in the case of nonluminous, perceived colors is called the spectral reflectance q (2). After defining three reference stimuli, the trichromatic principle allows a three-dimensional color space to be built up in which the color coordinates (tristimulus values) can be interpreted as components of a vector (CIE system for standards, see Table 1, Colorimetry CIE = Commission Internationale de l Eclairage). For uncolored illumination the three CIE tristimulus values depend on the spectral reflectance as follows ... 

The International Commission on Illumination (CIE) International Commission on Illumination (CIE) has defined a set of standard illuminants to be used for colorimetry (International Commission on Illumination 1996). Figure 3.21 shows the CIE illuminants A, C, Z>5o, Z>55, Z>65, and D15. Illuminant A represents the power spectrum of light from a black-body radiator at approximately 2856 K. If this type of light is required for experiments, a gas-filled tungsten filament lamp that operates at a temperature of 2856 K is to be used. Illuminant Z>65 represents a phase of daylight with a correlated color temperature of approximately 6500 K. The CIE recommends to use this illuminant wherever possible. 

The L a b color space is a visually uniform color space and is quite useful for designing devices suitable for visual colorimetry. The angle originating from the positive direction of the a axis expresses the hues themselves and is defined as the hue angle, hab, expressed by Eq. 29 [13] ... 

Colorimetry/photometry exploits the fact that the color intensity of the complex correlates to the metal ion concentration, at least within a certain concentration range. Therefore, sufficient indicator is added to the sample that the indicator forms a colored complex with all ions of the metal of interest in solution. The color intensity of this complex is then either compared visually against the color of reference samples (colorimetry) or the color intensity is measured at a defined wavelength with an instrument and then compared with a calibration curve (photometry). 

The problem of evaluating the color of a commercial sugar product must first be defined in recognized colorimetric terms. Colorimetry is a... 

The basic definition of reflectance, as used in colorimetry, is the ratio of the light flux reflected from a material to the light flux incident on the material. Reflectance involves accounting for all of the visible radiation in the system. This is in contrast to a reflectance factor, which is defined as the ratio of the light flux reflected from a material to light flux reflected from a standard material [23], Material standards of reflectance and transmittance are difficult to obtain. Reflectance, in particular, is difficult since the primary standard of reflectance is the perfect reflecting diffuser,... 

The CIE is an international body which coordinates worldwide cooperation and exchange of information on matters relating to illumination, colour, vision and image technology. It is recogtused as an international standardisation body, and has defined and standardised several colour spaces. For more information on the CIE and the CIELAB colour space (an internet search on the term CIELAB will produce thousands of additional links) http /Avww.cie.co.at/ [accessed July 2011] ISO 11664-4 2008(E), CIE Colorimetry — Part 4 1976 L a b Colour Space, CIE, Vienna. 

Colorimetry—An analytical method by which the amount of a compound in solution can be determined by measuring the strength of its color by either visual or photometric methods. Combustible— Term used to classify certain liquids that will burn on the basis of flash point NEPA and DOT classify combustible liquids as having a flash point of 100°F (38°C) or higher. Combustible liquids—OSHA defines combustible liquids as any liquid having a flash point at or above 100°E (38°C) but below 200°E (93.3°C). 

Five important treatises on color have appeared in recent years. Handbook of Colorimetry (Hardy, 1936) is a direct outcome of the eighth session of the International Commission on Illumination in 1931. It enables us to compute psychophysical values for brightness (later termed luminous refiectance and now, lightness) and chromaticity (dominant wave length and purity) from the raw spectrophotometric data. In these psychophysical terms, a colored sample may be uniquely defined with respect to its color, provided that we follow a standard procedure for determining the spectral refiectance or transmittance of the sample. The perceived color, however, is not defined, and we enter here into psychological considerations as distinct from those of psychophysics. The C.I.E. quantities x and y (the trichromatic coefficients which... 

The latest of the five treatises discussed here is entitled The Science of Color by the Committee on Colorimetry of the Optical Society of America (1953). A slight letdown is possibly inevitable, which a rereading does not entirely banish. The report is designed to include an elementary discussion to attract and hold the attention of casual readers, with a gradual transition to more advanced exposition. The food technologist tackling the psychophysics of color is apt to be impatient when confronted with distinctions between operational and relational definitions. He learns that the use of quantitative concepts would specialize the relational definitions in an undesirable manner loc. cit, p. 220). Continued study makes the reader more aware of the problems facing the Committee. Is color to be defined as a sensation or in terms of perception How many attributes of color are to be admitted ... 

Beside visual assessment, the color of an object can be characterized more precisely in terms of mathematical models, which are based on the remission and transmission spectra in the visible light area [6]. The most common CIELAB system, defines a color space and allows one to describe a specific color in terms of L (lightness) and the color coordinates a and b, and color differences or tolerances by related AL, A Ab and a combined AE value. L, a, b, values can be transformed into the probably more convenient terms of L (lightness), h (hue) and c (chroma). Today, colorimetry software is used for color matching and allows very precise calculations of pigment formulations. 

Since 1931, the most widespread color spaces for colorimetry of luminescent materials are based on the CIE XYZ color space. The CIE (commission intemationale de I eclairage) is an organization that standardizes all the color sciences. Here, X, Y, and Z coordinates represent a defined combination of R, G, and B so that the sensitivity function that defines the Y coordinate fits the photopic sensitivity of the eye (average sensitivity function of the... 

An important point about colorimetry is that all the standard color spaces use relative radiometric units and not relative photon counts. This is important because a spectrophotometer usually measures counts that are proportional to the number of received photons at a defined wavelength. A correction fimction that performs at the same time the correction of the detector sensitivity at each wavelength as well as the conversion to radiometric units is then needed... 

For many apphcations, particularly the more scientific or technical, detailed knowledge of the full transmittance and reflectance spectra of the glass may be important. Such information can be obtained by using UV, visible, and infrared spectrophotometers. For other applications, consistent color matching of different lots of product, often to a well-defined target, is sufficient. Here the science of colorimetry is important. The observed color of an... 

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