Light Sources and Illuminants Questions and Answers

Answer: A

The lamp trade uses these descriptions consistently across manufacturers. They describe the appearance of the source rather than its rendering quality. Rendering is reported separately again. Appearance and rendering are distinct properties.

Answer: B

The reference is a blackbody or a daylight illuminant of the same correlated colour temperature. Shifts in a set of test colour samples are averaged into a single figure. The reference changes with the source temperature.

Answer: C

It means no shift in any of the test samples relative to the reference. A blackbody radiator scores one hundred against itself by definition. The comparison is essentially with itself. A perfect score says little about usefulness.

Answer: D

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. Below 5000 K the colour rendering index compares the source with a blackbody at the same correlated colour temperature, and a tungsten lamp very nearly is one. It therefore scores about 100 by construction - a fact that shows how the index should be read: as fidelity to a reference, not as a measure of light quality in the abstract.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 describe the method correctly: the reference is a blackbody or a daylight phase at the source’s own correlated colour temperature, and 100 means the test samples shift not at all. Statement 3 claims too much - the eight standard samples are all of moderate saturation, so a source can score highly and still render strong reds badly.

Answer: B

Averaging over eight unsaturated samples can conceal a severe shift in a saturated one. Narrow band sources are flattered by the method more than they deserve. Eight pastel samples reveal too little. Saturated colours expose what averaging conceals.

Answer: C

Both are true and the reason gives the weakness, and the special samples R9 to R14 were added for this reason. The R9 red value in particular is frequently quoted separately. Strong reds expose the weakness most clearly.

Answer: D

Strong reds are where narrow band sources most often fail badly. A high general index with a poor R9 is a recognised warning sign. Strong reds are where narrow band sources fail. A poor R9 undermines a good general score.

Answer: A

Correct answer: using many more samples and reporting fidelity and gamut separately

TM-30 answers the two main criticisms of the older index. It uses 99 samples covering the colour space and the range of real object spectra rather than eight pastel ones, and it separates fidelity, meaning how little colours shift, from gamut, meaning whether they are rendered more or less saturated - two things the single index conflated.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: many more samples, and fidelity and gamut reported separately. Statement 3 is wrong - TM-30 still compares against a reference at the source’s own correlated colour temperature, exactly as the colour rendering index does. What it changes is the sampling and the reporting, not the principle.