Luminous reflectance

Methods are described for determining the extent to which original natural color is preserved in processing and subsequent storage of foods. Color differences may be evaluated indirectly in terms of some physical characteristic of the sample or extracted fraction thereof that is largely responsible for the color characteristics. For evaluation more directly in terms of what the observer actually sees, color differences are measured by reflectance spectrophotometry and photoelectric colorimetry and expressed as differences in psychophysical indexes such as luminous reflectance and chromaticity. The reflectance spectro-photometric method provides time-constant records in research investigation on foods, while photoelectric colorimeters and reflectometers may prove useful in industrial color applications. Psychophysical notation may be converted by standard methods to the colorimetrically more descriptive terms of Munsell hue, value, and chroma. Here color charts are useful for a direct evaluation of results. 

Marked changes occur in the visible appearance of dehydrated foods with variation in particle size. It has been found that this effect is chiefly one of variation in luminous reflectance, Y (see Tables I and II). In some instances (note the data for cabbage), chromaticity (x, y) remains so nearly constant over a fairly wide range of particle size that it appears possible that for certain products and purposes the effect of particle size might be eliminated by the choice of chromaticity as a color variable. 

The spectral characteristics of the source, photocells, and the three filters are such that approximate I.C.I. tristimulus values may be calculated (5) and from these a specification in terms of luminous reflectance, dominant wave length, and purity can be obtained. Hardy has cautioned (3), however, that the usefulness of such an instrument as a tristimulus colorimeter depends upon the standardization and constancy of the spectral characteristics of the light source, cell, and filters. 

In terms of the chromaticity diagram, it can be said that two colors having the same chromaticities (x,y) and the same luminous reflectance (Y) are matched. Technically, no information is provided about the appearance of two matched colors, although subjective judgements about specific colors identified by a pair of (, y) corrdinates are often made. 

A Hardy-type spectrophotometer may be used for determining luminous reflectance, transmittance, and color of polymers (ASTM-791). The transmittance of plastic films is measured by ASTM-D1746. 

From a consideration of the colour solid it is apparent that there is a maximum possible luminous reflectance or transmission for any specific colour value. The gamut of possible colour values diminishes as the Y value approaches 1, and a few discontinuous steps in the relationship between chromaticity and maximum luminance with standard source Sc are shown in Fig. 26.18. An interesting feature is that the highly saturated reds, yellows, and oranges situated near the spectrum loci boundary in the... 

Fig. 7. (a) OLED design (b) calculated reflectance (solid line) with the photopic curve (dash line) and the value of the luminous reflectance RD (c) refractive index profile (step) and irradiance profile inside the OLED, with the arrows showing the metal layers, and the emitting layer marked in black. 

Opacity to BS 4432 1980 Parts 1 and 2 (95) ISO 3688. This is the ratio, expressed as a percentage, of the luminous reflectance factor of a single sheet of the paper with a black backing to the intrinsic luminous reflectance factor of a layer, or pad, of the same paper which is thick enough to be opaque. 

Translucent suspensions are difficult to measure, and direct nnobserved interpretation of instrumental data can lead to confusion because of the way the incident light is dispersed in the sample. Most consistent results are obtained if the instrument aperture is large relative to the incident beam (Kent 1987 MacDougall 1987). The effects of optical geometry on colom and the Kubelka-Munk absorption K (mm ) and scatter S (nun ) coefficients for orange juice were studied by MacDougall (1983) who foimd Too, the luminous reflectance at calculated infinite thickness, increased by 50 per cent if the aperture diameter was increased from 2 cm to 5 cm while the incident beam was maintained at 1 cm. 

The relative luminous reflectance factor of a specimen at the specular direction. 

Contrast ratio n. (1) Ratio of the reflectance of a dry paint film over a black substrate of 5% or less reflectance, to the reflectance of the same paint, equivalently applied and dried, over a substrate of 80% reflectance. (2) The ratio of the luminous reflectance, Y measured on a film over a black... 

Luminous lu-m3-n9s [ME, fr. L luninosus, fr. lumin-, lumen] (15c) adj. (1) Adjective used to imply dependence on the spectral response characteristic of the Standard Observer defined in the CIE System. Thus, the luminous reflectance or the luminous transmittance is described by the Y-tristimulus value in the CIE System. The adjective is applied to many measures of light, such as... 

Y n. Abbreviation. (1) Chemical symbol for the element yttrium, which has been used as a catalyst for ethylene polymerization. (2) One of the three CIE tristimulus values, equal to the luminous reflectance or transmittance the green primary. 

Requirement (5) is satisfied by incorporating ATO (antimony tin oxide) particles in the bottom layer. The size of the particles should be small enough to keep the transparency of the film the particle size below 100 nm is needed. Furthermore, for the reason that these conductive particles have a high reflectivity and have no adhesion to the Si02 matrix, the addition is limited to the bottom layer, hi this design, the poor adhesion is compensated with the top layer and the high reflectance can contribute to the luminous reflectance improvement. 

LR. Luminous reflectance Measured by Multicannel Photodefector MCPD-2000 OTSUKA ELECTRONICS. 

Contrast Ratio m (1) Ratio of the reflectance of a dry paint film over a black substrate of 5% or less reflectance, to the reflectance of the same paint, equivalently applied and dried, over a substrate of 80% reflectance. (2) The ratio of the luminous reflectance, Y measured on a film over a black substrate, to the Y measure on the same film over a white substrate. The Y of the white and black must be specified. The contrast ratio will vary depending on the thickness of the film and on the concentrations of colorants (Sward GG (ed) (1972) Paint testing manual physical and chemical examination of paints, varnishes and lacquers, and colors, 13 th edn. ASTM Special Technical Publication No. 500, American Society for Testing and Materials, Philadelphia). 

Gloss is defined as the relative luminous reflectance factor of a specimen at the specular angle. Gloss is a function of the reflectance and the surface finish of a material, which, in turn, depends on the finish of the mould. 

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