Colour measurement instruments typically report reflectance at intervals of
Answer: A
Ten and twenty nanometre intervals are both common in industrial instruments. Finer intervals bring little benefit for smooth reflectance curves. Ten and twenty nanometre intervals are both common. Either suffices for a smooth curve.
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Assertion (A): A ten nanometre interval is adequate for most colourant reflectance curves.
Reason (R): Such curves are smooth and contain no narrow features to be missed.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the justification. A sampling interval must be fine enough to follow the fastest change in the curve, and the reflectance curves of ordinary colourants are broad and smooth, so ten nanometres captures them. A source with narrow emission lines is a different matter and needs a much finer interval.
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Consider the following statements about wavelength interval.
1. Smooth reflectance curves are adequately sampled at ten nanometres.
2. Narrow band emission requires a much finer interval.
3. A finer interval always improves the measured colour values.
Answer: C
Correct answer: 1 and 2 only
Statements 1 and 2 are correct: smooth curves are adequately sampled at ten nanometres and narrow band emission is not. Statement 3 is wrong - once the interval is fine enough to follow the curve, reducing it further adds nothing but noise and measurement time, since there is no structure left to resolve.
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The wavelength range of a colour measuring spectrophotometer typically covers
Answer: D
Instruments measuring fluorescent samples extend further into the ultraviolet. The visible range is the minimum required for tristimulus calculation. Fluorescent work extends into the ultraviolet. The visible alone suffices for ordinary samples.
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Wavelength accuracy of a spectrophotometer is verified using
Answer: A
Holmium or didymium filters provide sharply defined absorption bands. A wavelength error shifts every reading and corrupts the computed values. Holmium and didymium filters are used for the check. Their absorption bands are sharply defined.
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Assertion (A): A wavelength scale error affects every measurement the instrument makes.
Reason (R): Reflectance is attributed to the wrong wavelength throughout the spectrum.
Answer: B
Correct answer: Both A and R are true, and R is the correct explanation of A
Both are true and the reason gives the mechanism. If the wavelength scale is displaced, every reflectance value is recorded against the wrong wavelength, so the whole curve is shifted and every tristimulus value computed from it is wrong. The error is systematic and appears in every measurement, which is why the wavelength scale is checked with a filter having sharp absorption bands.
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Photometric accuracy of an instrument refers to
Answer: C
Correct answer: the correctness of the reflectance scale it reports
Photometric accuracy concerns the vertical axis: whether a surface of 40 per cent reflectance is reported as 40 per cent. It is checked with grey tiles of certified reflectance spanning the range. Wavelength accuracy concerns the horizontal axis, and repeatability is a separate property again - an instrument can be repeatable and inaccurate at once.
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Match each instrument performance characteristic with its check.
List I
A. Photometric scale
B. Wavelength scale
C. Zero and stray light
D. Repeatability
List II
1. a black trap at the measuring port
2. grey tiles of certified reflectance
3. repeated readings on a stable tile
4. a filter with sharp absorption bands
Answer: D
Correct answer: A-2, B-4, C-1, D-3
Each characteristic has its own check. The photometric scale is verified with grey tiles of certified reflectance, spanning the range rather than only the white end. The wavelength scale is checked with a filter having sharp absorption bands at known positions. Zero and stray light are checked with a black trap. And repeatability is measured by repeated readings on one stable tile.
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Inter-instrument agreement describes
Answer: A
It is quoted as a mean colour difference from a set of reference tiles. It limits how well measurements can be shared between sites. It is quoted as a mean difference over reference tiles. Specifications state it explicitly.
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Assertion (A): Colour data shared between two sites should ideally come from profiled instruments.
Reason (R): Inter-instrument differences would otherwise be mistaken for real colour differences.
Answer: B
Both are true and the reason gives the risk, and the difference can exceed the tolerance itself. Profiling to a master instrument is the usual remedy. Differences can exceed the tolerance itself. Profiling reduces them considerably.
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