An Instrument To Measure The Color-Determining Properties Of Bulk Translucent Materials

Peter C.F. Borsboom; Jaap J. ten Bosch; Reinoud P.T. Koeman

doi:10.1117/12.949350

10 March 1989 An Instrument To Measure The Color-Determining Properties Of Bulk Translucent Materials

Peter C.F. Borsboom, Jaap J. ten Bosch, Reinoud P.T. Koeman

Proceedings Volume 1012, In-Process Optical Measurements; (1989) https://doi.org/10.1117/12.949350
Event: 1988 International Congress on Optical Science and Engineering, 1988, Hamburg, Germany

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. L_c, 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 L_c and L_e, 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 L_c. 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 L_c and L_e increased with s(1-g), reached a maximum and decreased. The maxima for L_c and L_e were at s(1 g) = 1 and 0.06 mm -1, respectively. At a constant scattering, increase of absorption decreased L_e much stronger than it did L_c. 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 L_e. 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 L_c and L_e 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.

Citation Download Citation

Peter C.F. Borsboom, Jaap J. ten Bosch, and Reinoud P.T. Koeman "An Instrument To Measure The Color-Determining Properties Of Bulk Translucent Materials", Proc. SPIE 1012, In-Process Optical Measurements, (10 March 1989); https://doi.org/10.1117/12.949350

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