Light Sources and Illuminants Questions and Answers

Answer: A

The first two are correct and describe two separate properties. The third is generally the reverse, since concentrating emission where the eye is sensitive raises efficacy but leaves gaps. The two properties frequently pull against each other.

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. Efficacy in lumens per watt rewards emission near 555 nm, where the eye is most sensitive, so the efficient design concentrates output there. Rendering requires power across the whole visible range, so the two pull against each other - and the sodium lamp is the extreme case of choosing efficacy.

Answer: C

Correct answer: emits at essentially a single yellow wavelength

Low pressure sodium emits almost entirely in the sodium D lines near 589 nm, so there is simply no light at other wavelengths for an object to reflect. Everything appears as a shade of yellow or grey, and the rendering index is negative. It is used only where seeing detail matters more than seeing colour, as on some roads.

Answer: D

Low pressure sodium is the standard example of exactly this combination. Efficacy and rendering measure entirely different properties. A high figure in one implies nothing about the other. They answer entirely different questions.

Answer: A

A brightened sample measured with too little ultraviolet appears less white than it is. Instruments provide adjustable filters so the ultraviolet can be set to match the reference illuminant. Calibration is against a reference fluorescent standard.

Answer: B

Both are true and the reason gives the necessity, and the filter is calibrated against a reference standard. Without adjustment results are not comparable between instruments. Adjustment must precede any brightened measurement.

Answer: C

The first two are correct and matter greatly for brightened goods. The third is only true for samples containing no fluorescent material at all. Brighteners are present in most white goods. Textiles and papers are brightened almost universally.

Answer: D

Correct answer: how closely they match the defined daylight illuminant

A simulator is judged by how nearly its spectrum reproduces the illuminant it stands in for, not by its power, its temperature or its life. The grading is expressed through metamerism indices computed over the visible range and separately over the ultraviolet, since the latter governs how brightened samples appear.

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 mechanism. Pairs of samples are defined that would match exactly under the true illuminant; the colour difference they show under the simulator measures the residual mismatch. Grades run from A for the closest to E, and a separate index covers the ultraviolet region.

Answer: B

Correct answer: it was adopted as the standard viewing condition for print

The choice is a convention rather than a technical superiority. The graphic arts settled on D50 and the standards for proofing and viewing booths follow it, so a print judged elsewhere may not be judged as its industry judges it. Textiles equally conventionally use D65, and neither is more correct than the other.