Is tube light/fluorescent lamp monochromatic or polychromatic? Please justify.

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    $\begingroup$ Have you tried Google? $\endgroup$ – Hunter Jan 25 '14 at 15:25

As you can see from the plots of spectra of different fluorescent lamps as given here, you can definitely say: yes, it's certainly polychromatic.

Moreover, true monochromatic light is an abstraction, which can't be implemented in a real device, because it's the light infinite in time - from infinite past to infinite future. It is a limit, which can be approached instead. One of the most monochromatic light source is laser. Even better one is the filtered output of certain electron transitions. Such devices are used to e.g. define unit of distance.

  • $\begingroup$ Well, to be nitpicky, the most monochromatic device is the filtered output of certain electron transitions, as once use used in the definition of distance: en.wikipedia.org/wiki/… $\endgroup$ – Carl Witthoft Jan 25 '14 at 17:25
  • $\begingroup$ @CarlWitthoft can't $^{86} \text{Kr}$ be made one of active gases of a gas laser? ;) $\endgroup$ – Ruslan Jan 25 '14 at 17:28
  • $\begingroup$ Yes it probably could, but then you run into Lamb dips, pressure broadening, and all the other stuff that happens in any gas laser. $\endgroup$ – Carl Witthoft Jan 25 '14 at 17:30
  • $\begingroup$ @CarlWitthoft thanks, I've edited my answer to include your device. $\endgroup$ – Ruslan Jan 25 '14 at 17:35

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