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?