Light Sources and Illuminants Questions and Answers

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 record the two conventions correctly. Statement 3 is the misconception behind most illuminant disputes - there is no universally correct illuminant, only the one an industry has agreed on or the one under which the product will actually be seen.

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. Where samples differ spectrally, the illuminant decides whether they match, so a batch accepted under the supplier’s lighting can be rejected under the customer’s. Naming the illuminant in the specification is what makes the acceptance test mean the same thing at both ends.

Answer: A

Correct answer: detect metamerism between the sample and the standard

A single illuminant reveals only whether the pair matches under that light. Assessing under a second exposes whether the match survives a change of illuminant, which is precisely what metamerism is. Two assessments is the practical minimum, and retailers commonly specify daylight together with their own store lighting.

Answer: B

Reflectance belongs to the object rather than to the source. The other three are all source properties derived from its spectral power distribution. Reflectance belongs to the object instead. Source and object properties must be kept apart.

Answer: C

Its deficiency in the ultraviolet made it unsuitable once fluorescent brighteners became common. The D series was derived from measurements that included the ultraviolet region. Brighteners made the deficiency untenable.

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. Illuminant C was defined before fluorescent whitening agents were in general use and carries too little ultraviolet to represent daylight where they are present. A brightened sample therefore looks quite different under C from how it looks outdoors, and the D series was introduced with a realistic ultraviolet content to replace it.

Answer: A

Correct answer: 6504 kelvin

D65 is defined at a correlated colour temperature of about 6504 K - the number in its name being the temperature in hundreds of kelvin, rounded. D50 at 5003 K and illuminant A at 2856 K complete the set most often met in practice.

Answer: B

Both are true and the reason gives the history, and the name was retained for continuity. The same applies to D50 and D75 in the same series. A constant revision shifted all three slightly. Names were retained for continuity of usage.

Answer: C

Pairs that match exactly under the reference are measured under the simulator. Any resulting colour difference is the residual mismatch being quantified. Perfect simulation would give a zero index. Residual mismatch is what the grade reports.

Answer: D

Each is chosen because it represents the conditions the product will meet. Specifying more than one is normal where the end use is varied. Each represents a condition the product will meet. End use determines which are appropriate.