Metamerism illuminant

Clearly, standardized light sources are desirable for color matching, particularly in view of the phenomenon of illuminant metamerism described below. Over the years CIE has defined several standard illuminants, some of which can be closely approximated by practical sources. In 1931 there was Source A, defined as a tungsten filament incandescent lamp at a color temperature of 2854 K. Sources B and C used filtering of A to simulate noon sunlight and north sky daylight, respectively. Subsequently a series of D illuminants was estabUshed to better represent natural daylight. Of these the most important is Illuminant E). ... 

Quantification of metamerism is difficult and its avoidance is a principal aim in color technology. The car where body color, upholstery, and plastic parts match in the Ht showroom should not show clashing colors in daylight. The obvious but rarely appHcable solution is to use the same pigments in all parts. Some illuminant metamerism is almost unavoidable, the aim of the color expert being to keep it within acceptable limits, ie, to achieve adequate color consistency. 

Color-order systems, such as the many MunseU collections available from Macbeth, have been described previously. Essential for visual color matching is a color-matching booth. A typical one, such as the Macbeth Spectrahte, may have available a filtered 7500 K incandescent source equivalent to north-sky daylight, 2300 K incandescent illumination as horizon sunlight, a cool-white fluorescent lamp at 4150 K, and an ultraviolet lamp. By using the various illuminants, singly or in combination, the effects of metamerism and fluorescence can readily be demonstrated and measured. Every user should be checked for color vision deficiencies. 

When Munsell devised his color space, he did so on the basis of minimum observable color perception steps. But the problem with the Munsell System was one of reproducibility, which the CIE Standard Observer cured. In formulating a color match, one wants to be able to predict the correct concentration of colorants required, whose scattering and absorption properties are known, i.e.- the lightness, so as to match the sample submitted, starting with their spectrophotometric curves. In practice, this is not so simple, since two colors must have identical spectrophotometric curves to be exactly equal. It turns out that the human eye will identify the two colors to be equal if their spectrophotometric reflectances are reasonably close. Two colors may appear to be equal under Daylight illumination, but quite different under incandescent lamp illumination. These colors are known zus "metamers" and the phenomenon "metamerism". 

Metamerism is a change of colour under different illuminants. 

The importance of the light source and other conditions that affect viewing of samples cannot be overemphasized. Many substances are metameric that is, they may have equal transmittance or reflectance at a certain wavelength but possess noticeably different colors when viewed under illuminant C. 

Where assessments take place on a production line, good consistent conditions for viewing the sample or matching to a memorised or formal colour standard need to be made available. Market researchers often find themselves in conditions unsuitable for the making of reliable appearance assessments. A specification of the environment of the test, including types of illumination and colour of the test surrounds, should be noted in the final report. This will make it easier for the occurrence of colour metamerism problems to be minimised. If the consumer s views of product colour and appearance are important to the project, standard lighting and viewing conditions should be provided. 

It should always be borne in mind, however, that if a subjective assessment of the colour of a particular food is normally carried out under, say, a tungsten filament light or under direct sunlight, then it may be preferable to carry out the instramental measurement under similar lighting conditions. It should be noted also that a pair of samples which colour-match another under one illuminant may not match under a different illuminant. This phenomenon is known as metamerism and is of great importance to those in the textile and paint industries. 

Index of metamerism -mo- ta-mo- ri-zom. An index to describe the degree of metamerism existing between two samples. There is no standard accepted index. However, a frequently computed index is the color difference, using a specified equation, which exists under a second illuminant when a pair of colors is an exact match under a primary or first illuminant. 

Matching, color n. Act of making one material appear to match another color. If the achieved match is dependent on the conditions of illumination and viewing, the match is termed conditional or metameric. If the achieved is independent of the quality of the illuminant viewer, or viewing conditions, the match is termed nonconditional or non-metameric. 

Metameric pair n. A pair of colors, which match when viewed in a described way but which do not match if the viewing conditions are changed, thus, a metameric pair of samples exhibit the same tristimulus values for a described set of viewing conditions (observer, light source, geometry of the illumination, and viewing arrangement) but have different spectral distributions. Hence, they exhibit a match, which is conditional only. 

The interplay of these criteria is well illustrated by the two main classes of compound that have historically dominated the development of anisotropic dyes. Azo dyes tend to offer better order parameters, larger extinction coefficients, and better solubility in liquid crystals, whereas the anthraquinone materials tend to have better photochemical stability. The position now is that following a number of years of intensive development stable anisotropic dyes in a variety of colors are available commercially. Colors may be mixed to give black, high-order-parameter mixtures. Note that such blacks are metameric and in principle will change hue with changes in the illuminant, although in practice very acceptable mixtures can be obtained. 

Metameric Colours. Colours that appear to be the same under one type of illuminant but, because they have different spectral reflectivity curves, will not match under a different illuminant. Two white vitreous enamels may be metameric, for example, if one is opacified with titania in the anatase form whereas the other contains titania in the form of rutile. Methuselah. A 9-quart wine bottle. Methylene Blue Index A simple approximate method for assessing the surface area of a clay. O.OIM methylene blue dye is added to aqueous suspension of clay, in successive small amounts, to determine the least amount of dye required to impart colour to the water suspending the clay. Dye up to this amount is absorbed by the clay, so that this is a measure of the clay s cation exchange capacity (see ionic exchange). For most pottery clays this is proportional to the surface area to a good approximation. ASTM C837 specifies a test for clays. 

Metamerism Occurs when a colorant takes on a different perceived color based on a change in illumination. 

This scenario is a common occurrence in plastics and other industries. The reason is very simple. Two objects having the same color, when viewed under one type of illuminant (daylight), appear to match. The same two objects when viewed under different types of illuminants (incandescent) do not match. This phenomenon is known as metamerism. Metamerism is a phenomenon of change in the quality of color match of any pair of colors, as illumination or observer or both are changed. 

Has many available observer/illuminant combinations that can be used for calculating tristimulus data and metamerism index. 

Works well for color formulation, measurement of metamerism, and variabie illuminant/observer conditions. Optimal for both quality inspection and research and development. 

Metamerism Metamerism is a phenomenon of change in the quality of color match of any pair of colors as illumination or observer or both are changed. 

Metamerism (1) Phenomenon whereby lights of different spectral power disfributions appear to have the same color. (2) Degree to which a material appears to change color when viewed under different illuminants. 

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