A spectrophotometer differs from a tristimulus colorimeter in that the spectrophotometer
Answer: A
Spectral data allows values to be recomputed for any illuminant and observer. A colorimeter commits to one condition at the moment of measurement. Spectral data can be reprocessed at any time. Nothing need be decided at the moment of reading.
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Assertion (A): Spectral measurement is preferred to filter colorimetry in industry.
Reason (R): The spectral data can be recomputed for any illuminant and observer afterwards.
Answer: B
Both are true and the reason gives the advantage, and metamerism can also be assessed. A filter colorimeter cannot answer questions that were not anticipated at the time of measurement. Metamerism assessment needs the full spectrum.
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Consider the following statements comparing the two instrument types.
1. A spectrophotometer records reflectance across the spectrum.
2. A colorimeter records three filtered readings only.
3. A colorimeter can compute values for any illuminant afterwards.
Answer: C
The first two are correct and describe the two designs. The third is impossible, since the filters fix the illuminant and observer at the moment of reading. Filters cannot be changed after the fact. The condition is fixed by the hardware itself.
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Match each instrument component with its function.
List I
A. Light source
B. Monochromator or filters
C. Detector
D. Integrating sphere
List II
1. converting the light into an electrical signal
2. illuminating the sample under measurement
3. collecting light from all directions
4. separating the light by wavelength
Answer: D
Correct answer: A-2, B-4, C-1, D-3
Four components in the order the light meets them. The source illuminates the sample; the monochromator or filter set separates the returned light by wavelength; the detector converts it into an electrical signal. The integrating sphere is the optional element that collects light from all directions, which is what makes diffuse geometry and the specular included measurement possible.
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The 45 degree to 0 degree measurement geometry illuminates the sample at 45 degrees and views it
Answer: A
Specular reflection at 45 degrees is directed away from the detector entirely. The geometry therefore always excludes the gloss component. There is no option to include it here. Sphere instruments alone offer the choice.
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Assertion (A): The 45 to 0 geometry always excludes the specular component.
Reason (R): The specular beam leaves at 45 degrees on the far side and misses the detector entirely.
Answer: B
Both are true and the reason gives the geometry, and there is no option to include it. Sphere geometries by contrast offer both possibilities in one instrument. A gloss trap provides the choice. Opening it lets the specular beam escape.
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Match each measurement geometry with its characteristic.
List I
A. 45 to 0
B. 0 to 45
C. d to 8 SCI
D. d to 8 SCE
List II
1. diffuse illumination, specular included
2. directional, specular always excluded
3. diffuse illumination, specular excluded
4. directional, specular always excluded
Answer: C
Correct answer: A-2, B-4, C-1, D-3
The two directional geometries, 45 to 0 and 0 to 45, place the illumination and the detection so that the specular reflection never reaches the detector, so the specular component is excluded by the geometry itself and cannot be included. The sphere geometries illuminate diffusely, and the specular component is then included or excluded according to whether the gloss trap is open.
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The specular component included measurement is preferred when
Answer: D
Correct answer: assessing the colourant itself independently of the surface finish
Including the specular component means the reading depends much less on how glossy or matt the surface happens to be, so two samples of the same colourant with different finishes give similar values. That is what a formulator needs. Excluding it gives the reading that corresponds to how the sample looks, which is what an appearance judgement needs.
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Assertion (A): Specular included measurement is preferred for colourant formulation.
Reason (R): It reduces the influence of surface finish on the reading obtained.
Answer: A
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the argument. A formulator is concerned with the colourant, not with the finish that happens to be on this particular sample, and the specular included measurement largely removes the effect of surface texture and gloss. The specular excluded measurement is preferred for appearance work, where that effect is precisely what matters.
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Consider the following statements about specular component.
1. Included measurement reduces the effect of surface finish.
2. Excluded measurement correlates better with visual appearance.
3. The two give identical results on a glossy sample.
Answer: B
The first two are correct and describe the two uses. The third is quite wrong, and the difference on a glossy black sample is very large. Gloss dominates the reading in that case. A matt sample shows far less difference.
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