NCIDQ IDFX Practice Exam

What can improve the color rendering of mercury vapor lamps?

1. Adding phosphors to the arc tube.

2. Using lower pressure mercury.

3. Increasing lamp size.

4. Lowering the operating temperature.

The correct answer is: Adding phosphors to the arc tube.

Adding phosphors to the arc tube is effective in improving the color rendering of mercury vapor lamps. Mercury vapor lamps by nature have a limited color spectrum, producing a bluish-white light that often does not render colors accurately. When phosphors are introduced into the arc tube, they absorb the ultraviolet (UV) light generated by the mercury vapor and re-emit it as visible light across a broader spectrum. This process helps to fill in the gaps of the original spectrum emitted by the mercury vapor, resulting in better color rendering and a more pleasant light quality. While using lower pressure mercury, increasing lamp size, or lowering the operating temperature can have effects on the performance and efficiency of the lamps, they do not directly address the color rendering capabilities in the same way that adding phosphors does. Lower pressure might alter the light output, but it doesn't enhance the color spectrum. Increasing lamp size generally improves the uniformity of light distribution rather than color rendering. Lowering the operating temperature may affect efficiency and lifespan but does not inherently improve the spectrum of colors emitted. Thus, incorporating phosphors is a targeted method specifically aimed at enhancing color rendering for mercury vapor lamps.