Specular reflection, gloss

Certain industrial monitoring requires more than a single noncontact measurement. In order to characterize paper, for example, up to three optical heads can be directed at one measurement point, measuring in parallel the transmission, the specular reflectance (gloss), and the diffuse reflectance... 

The objective measure in this case is the intensity and kind of reflectance. Only for highly polished metal mirrors the reflectance may be nearly total if the specular reflectance is almost nil, the surface is totally matt. In between, the material is glossy or sheeny. Gloss is the reflectance of a surface responsible for its lustrous appearance, commonly at maximum near the specular direction, i.e. the direction of pure mirror reflection. 

Gloss is the percentage of incident light that is reflected at an angle equal to the angle of the incident rays (specular reflectance). It is a measure of the ability of a surface to reflect the incident light. Figure 3.56 illustrates a common procedure for... 

It is noted that the spectral characteristics of the light source are not critical unless highly chromatic low-gloss materials are tested or specular reflectance produces an obvious shift in the color of the incident light. It is also noted that if transparent materials are tested it must be possible to measure up to 200 gloss units. 

Despite the existence of the standard methods, differences can occur between difTerent gloss meters. Experts suggest that the lack of specification of the characteristics of illumination and of the photodetector is a source of more discrepancies than is indicated in the standards it is suggested that the illumination should be CIE illuminant C and the detector filtered to respond as the human eye. Other points are that for some materials the maximum specular reflection does not occur at the incidence angle, the test temperature and meter orientation should be the same as that for calibration, and there have been differences between working standards calibrated in different countries. 

Scratch hardness is particularly important in plastics used for their optical properties and is usually determined by some of mar-resistance test. In one type of test a specimen is subjected to an abrasive treatment by allowing exposure to a controlled stream of abrasive, and its gloss (specular reflection) is measured before and after the treatment. In some tests the light transmission property of the plastic is measured before and after marring. 

These instruments do not collect or incorporate the specular reflectance of a sample into the measurement. This measurement is typical of the view the human eye may have of a sample by excluding the specular energy. For example, when viewing a high gloss fype of sample you can usually determine a point where the reflection of the light is mirrored or reflected directly back at your eyes. This makes it difficult, as well as uncomfortable, to see any detail of the color of the sample. By tilting the sample either away from you or towards you, you can... 

In the classical polishing process the surface is smoothed to a mirror level, so that specular reflections can occur on opaque surfaces and be perceived as luster or gloss. In case of transparent materials, such as lenses, polishing minimizes the amount of incident light physically scattered by asperities and small defects. In both mentioned... 

Gloss Using a reflectometer by measurement of the specular reflectance for different angles of Incidence... 

Luster l9s-t3r [MF lustre, from 01 lustro, fr. lustrare to brighten, fr. L. to purify ceremonially, fr. lustrum] (ca. 1522) n. (1) Type of surface reflectance, or gloss, where the ratio of specular reflectance to diffuse reflectance is relatively high, but not so high as that from a perfect specular reflector (mirror). (2) Another term for gloss. 

Specular reflection n. Light striking a surface, and being reflected or turned back at an angle equal to the angle of incidence. See gloss. 

The subjective terms luster, gloss, and shine of hair are being used interchangeably in the literature, although shine is most meaningful to consumers (82). Subjective panel evaluations of this property can be quite accurate, if care is taken to keep fiber alignment, lighting, and certain panel considerations constant. However, to be able to make quantitative statements about the effectiveness of various treatments, efforts have been made to develop instrumental, objective methods of shine evaluation. All these methods (83-87) are based on the contrast between the intensity of the specularly reflected... 

Integrated areas of the goniophotometer curve yield numerical values for specular reflection (S) and diffuse seattering (D). Following the approach of Nickerson (88) for contrast gloss of cotton yams and fabrics, Stamm et al. used the following function to evaluate... 

One of the other definitions of luster or gloss (G), which has been proposed by Schulze zur Wiesche and Wortmann (89) and has also been explored at TRI (87), uses the ratio of the specularly reflected to the total reflected light ... 

OPAQUE METALS (Auto Bumper, Brass Doorplate) SPBCUUfl COLOR BY SPECULAR reflection Analyzed by Color Scal, Specular Gloss, Distir)clriesS Of>iinage Gloss, Luster, Directionality, or Surface Texture HAZE BY DIFFUSE REFLECTION Analyzed by Rtflaction Haze... 

Fig. IZ Specular transmission refers to light passing through an object without diffusion. Specular transmission measurements are widely used in the chemical analyses and color measurements of liquids. Potentially, appearance attributes important for specular transmission should be roughly analogous with gloss attributes associated with specular reflection (from HunterLab).

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