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Proceedings Paper

An Instrument To Measure The Color-Determining Properties Of Bulk Translucent Materials
Author(s): Peter C.F. Borsboom; Jaap J. ten Bosch; Reinoud P.T. Koeman
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Paper Abstract

A pencil beam incident on a translucent material causes a luminous circular spot of volume-reflected light. Its spectral radiance L (r) decreases with radius r. Lc, the value close to the centre is mainly determined by the scattering parameter s(1-g) of material. Le, the value at the edge of the spot, is determined by s(1-g) and the absorption coefficient a. The instrument (the CTM) employs three fibre bundles to measure Lc and Le, both as a function of λ (400-700 nm). A central bundle (2 mm p) of - 1300 fibres each of 50 um g is randomly divided in a bundle for illumination and a bundle for measurement of Lc. A concentric ring (i.d. 4 mm, o.d. 5 mm) of - 2500 fibres is used to measure Le. This instrument was tested with aqueous suspensions of latex and a dissolved, non-latex adsorbing, red dye. Thus s(1-g) (scattering) and a (absorption) could be independently varied. For a=0, both Lc and Le increased with s(1-g), reached a maximum and decreased. The maxima for Lc and Le were at s(1 g) = 1 and 0.06 mm -1, respectively. At a constant scattering, increase of absorption decreased Le much stronger than it did Lc. This absorption-caused decrease depended only weakly on the scattering coefficient: a variation of scattering of a factor 20 caused only a few percent change in absorption-caused decrease of Lc and only a factor 2 in absorption-caused decrease of Le. At s(1-g) = 0.3 mm-1, Le depended much more strongly on a than did the overall regular reflection spectrum of the suspension as measured with a Hunter spectrophotometer under 0°/45° geometry. The readings of Lc and Le with this instrument can be used to determine s(1-g) and a and the reflection spectrum. Only small samples are needed in comparison to the regular reflection spectrometry. To obtain absolute values the instrument has to be calibrated on the specific type of material under investigation.

Paper Details

Date Published: 10 March 1989
PDF: 6 pages
Proc. SPIE 1012, In-Process Optical Measurements, (10 March 1989); doi: 10.1117/12.949350
Show Author Affiliations
Peter C.F. Borsboom, Sensoptic (The Netherlands)
Jaap J. ten Bosch, University of Groningen (The Netherlands)
Reinoud P.T. Koeman, Sensoptic (The Netherlands)

Published in SPIE Proceedings Vol. 1012:
In-Process Optical Measurements
Kenneth H. Spring, Editor(s)

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