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Do salt lamps really produce negative ions? Do you know about any scientific study that could support this assertion or disprove it?

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Phrased as it is, i.e. essentially a reference request, I guess this would fit better on Skeptics.SE… – F'x Mar 18 '12 at 11:28
@truthseeker: do you want a hard reference or a scientific explanation from anyone? – Manishearth♦ Mar 18 '12 at 12:55
@F'x anyways, I'll mark it for migration. – Manishearth♦ Mar 18 '12 at 12:56
I dislike this question because it implies that 'negative ions' are something special and exotic, and that salt crystals might also be special and exotic. It's just a hunk of salt and an incandescent lamp! – nibot Mar 18 '12 at 18:14
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@nibot: 'negative ions' are special and exotic to almost everybody outside of science and engineering. – Alexander Mar 18 '12 at 19:53
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There is no study because there is no physical mechanism were a salt crystal sends negative ions into the air without any energy input. Just heating the inside up with an incandescent lamp warms the lamp a bit but this does not create any measurable amount of negative ions.

There are ion generators but these work on a completely different principle. Basically you need a very high electric field to ionize air molecules or dust particles. Here is a study that explains how the air quality is positively influenced by a air purifier that creates negative ions.

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Absence of proof vs. proof of absence… I agree with your answer for the physics, but there could be a study (and there probably is, somewhere) aimed at demonstrating that indeed, salt lamps heated with an incandescent lamp do not yield negative ions. – F'x Mar 18 '12 at 17:00
@F'x: I think it's quite unlikely. A scientific study is work- and time consuming and who would want to fund such an endeavour and it is hard to prove a negative anyway. – Alexander Mar 18 '12 at 17:12
Mechanism: "Some salt lamp manufacturers claim that the natural absorption of moisture and its subsequent release through the heating effect of the lamp, releases negative ions. Is this a fact?" – endolith Mar 19 '12 at 16:17
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@endolith: If a salt crystal becomes wet there will be a solution of Cl- and Na+ ions in water at the surface. The evaporation of Cl- ions in a water droplet is possible, that the whole droplet is negatively charged still unlikely. Reductio ad absurdum: A pot of boiling salt water would create a gigantic amount of negative ions. – Alexander Mar 19 '12 at 16:57
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This website addresses this issue. I have no idea how rigorous it is but it is interesting. http://www.negativeionsinformation.org/saltcrystallamps.html

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