This question has been causing a fair amount of controversy lately. Some people think it should be closed, some people think it should be opened. So I think we should get the community's input on it.

Is there a light source that emits all wavelengths of visible light at the same time?

How should this be dealt with?

The purpose of this meta question is only to establish the community opinion on what to do with the original question. This is not the place to discuss whether it is correct for a moderator to override a community vote, and it is not the place to discuss whether any of the comments posted or other actions taken were inappropriate.

Whatever opinion emerges from this meta question will be taken under advisement by the moderators (well, by me at least), but at this time I cannot promise that the original question will be opened or closed in accordance with what we decide here.


2 Answers 2


The question is short but I don't see why that matters.

It is also:

1) Specific - It displays a knowledge of some physics, i.e. that light comes in waves and is characterized by the wavelength; and that visible light has a bounded range of wavelengths.

2) About Physics - One can argue whether or not the question is too simple, but it is clearly on topic. The emission of light is clearly within the domain of physics.

3) Not Obvious - If you don't already know the answer, it is not obvious or deducible. If you happened to have just learned that photons come from electrons dropping energy levels which correspond to specific wavelengths of light, you might not yet realize that blackbodies (and light bulbs as one such example) emit a continuous spectra, or the reasons why they do this. This is not obvious physics even if it is generally taught in high-school.

Further, at times, even an easy question can have interesting answers. As Colin K. noted, there are broadband coherent light sources as well.

Do we really want to close as "off-topic" questions that can be easily answered as too easy? What kind of message does that send to the asker? You're stupid? Don't ask dumb questions?

I believe there is a reason that particular question was never updated by the asker. It was closed as being off topic very quickly and probably before the asker even returned to check for answers.

If this happened to me the first time I came here, I'd never bother coming back. I might just think to myself: "Physicists are real jerks" and never come back.

What possible harm is caused by questions of this sort? Are we saying that we don't want any high-school physics students here? Really?

What about engineers and other professionals that are 20 years out of school, do we assume they remember everything from their high-school and college physics so they know what is "trivial" and what is an "on-topic" question?

  • $\begingroup$ It has been decided that high school stuff is mostly off-topic here (unless it's non-trivial). If you want you can restart the discussion on this (perhaps community's opinion changed since last time) but this is the state of the matters and so closing high school question without any warning is no more wrong than closing any other off-topic question. $\endgroup$
    – Marek
    Commented Jan 13, 2011 at 9:04
  • 1
    $\begingroup$ @Marek - You don't happen to remember where that discussion took place do you? I'd like to read the thoughts there before commenting further. $\endgroup$
    – inflector
    Commented Jan 13, 2011 at 20:19
  • $\begingroup$ it was discussed all over the meta, I am not sure where precisely. Probably somewhere among these questions (the ones with lots of up-votes). $\endgroup$
    – Marek
    Commented Jan 13, 2011 at 22:40

Two separate issues with that question:

  1. It's short. This is not necessarily a problem. Some questions just are short. In this case I think the question could benefit by being made more precise but it's perfectly well answerable as it stands.

  2. But as pointed out by Sklivvz, it's a high school stuff. Well, perhaps not. Maybe it was intended an a research-level question asking about physical processes behind various sources of light (black bodies, QED and nuclear emission, properties of gases, semiconductors, whatever). But if so then OP needs to make that clear. Otherwise the answer is as short as, yes, it's called lightbulb and that's it. I don't think we need such a question.

In my opinion, the question should remain closed until OP (or someone else) makes it clear that it's non-trivial.

  • $\begingroup$ I disagree that being short is a real issue. It might have been a better question if it were longer, but it doesn't lack clarity and it's a very real question. I do agree with you and Sklivvz that it's high school stuff, which makes it off-topic until the OP elaborates. $\endgroup$
    – Malabarba
    Commented Jan 12, 2011 at 22:53
  • $\begingroup$ This is precisely the reason I closed it. Thanks for elaborating. $\endgroup$
    – Noldorin
    Commented Jan 13, 2011 at 1:24
  • 1
    $\begingroup$ @Bruce would you care reading my whole answer? Because you've just repeated what I had already written :-) $\endgroup$
    – Marek
    Commented Jan 13, 2011 at 9:06
  • $\begingroup$ Yeah =/. At first I wanted to emphasise I really don't think the first item is an issue (because a lot of people believe it is). Then I wanted to acknowledge it might be off-topic, because I had been defending it in the chatroom. Only later did I realise I sounded like a parrot. :-) $\endgroup$
    – Malabarba
    Commented Jan 13, 2011 at 14:06

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