A colour measured and reported without naming the illuminant is
Answer: A
Tristimulus values are computed from reflectance, illuminant and observer together. Reporting them without the illuminant leaves the reader unable to reproduce the calculation. Three numbers alone are not a specification.
Please log in or register to report this question.
Assertion (A): Spectral reflectance data is more portable than tristimulus values.
Reason (R): Reflectance is independent of the illuminant while tristimulus values are not.
Answer: B
Both are true and the reason gives the advantage, and tristimulus values can be recomputed from reflectance. Storing the spectral data preserves every future option. Recalculation for a new illuminant remains possible.
Please log in or register to report this question.
Consider the following statements about reporting colour data.
1. Spectral reflectance is independent of the illuminant.
2. Tristimulus values must be quoted with illuminant and observer.
3. Tristimulus values can be converted back to spectral reflectance.
Answer: C
The first two are correct and are the reason spectral data is preferred. The third is impossible, since the reduction from a spectrum to three numbers discards information. The reduction is irreversible by construction.
Please log in or register to report this question.
State whether the following is true or false.
Tristimulus values cannot be converted back into the original spectral reflectance curve.
Answer: D
Many different spectra give the same three numbers under one illuminant. This irreversibility is precisely what makes metamerism possible. Many spectra map to the same three values. The reduction discards information irrecoverably.
Please log in or register to report this question.
The eye's spectral sensitivity peaks in the photopic regime at approximately
Answer: A
The photopic luminous efficiency function peaks there and falls away either side. The scotopic peak sits near 507 nanometres, which is the origin of the Purkinje shift. Photopic and scotopic peaks differ by about fifty nanometres.
Please log in or register to report this question.
The scotopic luminous efficiency function peaks at approximately
Answer: B
Rod vision peaks at a shorter wavelength than cone vision does. The difference between the two peaks produces the Purkinje shift at twilight levels. Rods peak at a shorter wavelength than cones. The two peaks differ by about fifty nanometres.
Please log in or register to report this question.
Assertion (A): Lamps designed for road lighting are sometimes assessed with a mesopic weighting.
Reason (R): Road lighting levels lie between the photopic and scotopic regimes.
Answer: C
Both are true and the reason gives the reason, and photopic weighting alone misrepresents the situation. Mesopic models blend the two efficiency functions according to the level. Road lighting sits between the two regimes.
Please log in or register to report this question.
Flicker in a light source is a concern for colour assessment because it
Answer: D
Modulation at mains frequency or from a driver can be visible or subliminally troubling. High frequency electronic control gear is used in assessment cabinets for this reason. Modulation can be visible or subliminally troubling.
Please log in or register to report this question.
Lamp ageing affects colour assessment because
Answer: A
Correct answer: the spectral output drifts over the life of the lamp
Phosphors degrade and electrodes deposit material on the tube, so the spectrum of an ageing lamp is not what it was when new. Since every tristimulus value depends on that spectrum, assessments drift with it - which is why viewing cabinets record lamp hours and lamps are replaced on a schedule rather than when they fail.
Please log in or register to report this question.
Assertion (A): Viewing cabinet lamps are replaced on a scheduled basis.
Reason (R): Their spectral output drifts measurably over the operating life.
Answer: B
Both are true and the reason gives the necessity, and an hours counter is normally fitted. Waiting for visible failure would allow assessments to drift long beforehand. An hours counter is normally fitted for this purpose.
Please log in or register to report this question.
