Light Sources and Illuminants Questions and Answers

Answer: C

Correct answer: A-2, B-4, C-1, D-3

Four technologies with four distinct spectral signatures. Incandescence gives a smooth continuum weighted to the red. A fluorescent lamp gives a phosphor continuum with the mercury lines standing out sharply. Metal halide gives a continuum broken by the many lines of its metal additives. And a white LED gives the characteristic blue pump peak with a broad phosphor emission beside it.

Answer: D

The characteristic dip between the blue peak and the phosphor emission affects rendering. Improving the phosphor to fill that region is the main route to better rendering. The dip between peak and phosphor is characteristic.

Answer: A

Both are true and the reason gives the cause, and the R9 value was correspondingly low. Added red phosphors have largely remedied this in current products. Red phosphors fill the long wavelength gap. Current products render reds far better.

Answer: B

The first two are correct and describe the technology. The third is quite wrong, since the spectrum is markedly structured rather than smooth. A blue peak and a broad phosphor band dominate. The spectrum is structured rather than smooth.

Answer: C

The phosphor determines both the colour temperature and the rendering. Residual mercury lines remain visible as sharp peaks in the spectrum. Phosphor choice sets both temperature and rendering. Mercury lines remain visible as sharp peaks.

Answer: D

Efficacy improves considerably because light is placed where it is most useful. Rendering of saturated colours can suffer, since the spectrum has deep gaps between the bands. Efficacy is bought at the cost of the gaps.

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. Triphosphor lamps put their output into three narrow bands placed where the eye is most responsive, which is why they are efficient and score well on the standard index. But a saturated colour reflecting only between those bands has almost no light to reflect, so it renders poorly - a defect the eight pastel samples of the index barely register.

Answer: B

Twelve members cover halophosphate, broadband and triphosphor types. F11 in particular is widely used to test for metamerism under narrow band light. It represents a very common commercial lamp. Shop lighting is frequently of this type.

Answer: C

Both are true and the reason gives the reason, and it represents a common commercial lamp type. A pair matching under D65 may fail badly under F11. Shop lighting is frequently of this type. Testing under it exposes many practical failures.

Answer: D

It measures how effectively electrical power becomes visible light. It says nothing whatever about how well the source renders colours. Efficacy and rendering are quite separate measures. Neither can be inferred from the other.