Reflection visualization

Figire 46 (a) Calculated intensity distribution corresponding to tbe (102)/ (1-1-2) reflections visualized as intersection of the Polanyi (gray) and Ewald sphere (violet). Only a part of the Ewald sphere is shown in the figure for the sake of clarity, (b) Intersection between the Polanyi and Ewald spheres projected on the plane of a fiat 2D detector showing the azimuthal intensity distribution for the calculated (102)/(1-1-2) doublet reflection. 

Optical Properties. Brightness, or visual whiteness of paper, can be defined as the degree to which light is reflected uniformly over the visible spectmm. Since pulp and typical impurities tend to be yellowish, blue dye is sometimes added in addition to appropriate fillers. The percentage reflectance is usually measured in the blue end of the spectmm at or near 457 nm (14). 

Measurement of Whiteness. The Ciba-Geigy Plastic White Scale is effective in the visual assessment of white effects (79), but the availabihty of this scale is limited. Most evaluations are carried out (ca 1993) by instmmental measurements, utilising the GIF chromaticity coordinates or the Hunter Uniform Color System (see Color). Spectrophotometers and colorimeters designed to measure fluorescent samples must have reversed optics, ie, the sample is illuminated by a polychromatic source and the reflected light passes through the analy2er to the detector. 

Color. The visual color, from white to dark brown, of sugar and sugar products is used as a general indication of quaUty and degree of refinement. Standard methods are described for the spectrophotometric deterrnination of sugar color that specify solution concentration, pH, filtration procedure, and wavelength of deterrnination. Color or visual appearance may also be assessed by reflectance measurements. 

Optical Properties. When light falls on an object, it is either partially absorbed, reflected, or transmitted. The behavior of the object as it relates to each of these three possibiUties determines visual appearance. Optical properties of fibers give useful information about the fiber stmcture refractive indexes correlate well with fiber crystalline and molecular orientation and birefringence gives a measure of the degree of anisotropy of the fiber. 

Reflectance Spectrophotometry. Because of discrepancies that can occur between strength and shade evaluations in solution and on textile substrates, the latter is often the preferred evaluation technique. In the case of dye manufacture, many dyes are standardized in solution but there is always a final control step where dyeings are prepared. Historically, such dyeings have been evaluated visually for the relative strength and the shade of the dye under test on the substrate, compared to the standard. More and more attempts are being made to do such evaluations objectively. Guidelines for the use of this technique have been pubflshed (43). 

The success of separation of colored compounds is usually monitored visually. Such compounds absorb a particular portion of the polychromatic (white) light in the visible wavelength range. The remaining radiation (complementary radiation) is reflected and detected by the eye it determines the color of the substance zone. Table 1 correlates the wavelengths, colors and complementary colors. 

Radiant heat transfer had historically been the biggest heat transfer mechanism for windows. Low-e materials were developed and have historically been used to control for heat transfer. An example of the popularity of using metals to reflect heat to control for radiant heat transfer is the thermos bottle. Applying that new technology to windows, and getting materials that normally would affect transparency of the product to remain visually neutral, was a huge advance to the industry. 

Product quality control relates to appearance and methods of assessing it either by subjective visual inspection or by objective tests such as reflectivity or surface roughness. 

The indirect methods discussed thus far have dealt with measurement of color only as it can be correlated with physical characteristics of materials and the effect of these materials on radiant energy. As has been pointed out, the reflectance spectro-photometric curve describes a property of the material. A change in the reflectance spectrophotometric properties may not always result in a change in visual color. The reason is that color of the object is not an unchangeable characteristic of the object itself, dependent only upon these reflectance properties, but is also dependent upon the quality of the illuminating light and the sensitivity of the observer s eye. Thus the measurement and description of visual color are psychophysical problems... 

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