Salt lamps are marketed as being made of "Himalayan" salt, probably in order make them seem more New Age-y and spiritual. After all, Himalayan crystals must be chock full of mystical healing energy, as opposed to those mundane Western sodium chloride rocks, right? Actually, the term Himalayan salt is a bit of a misnomer, as it refers to salt from the Pakistani Khewra Salt Mine, which isn't actually in the Himalayas.
Negative ionic goodness
The problem with the claim that these lamps release negative ions is that electric lights and candle flames aren't nearly hot enough to break apart the ionic bonds between sodium and chlorine. As one university physics professor puts it, "If that were true, we'd have chlorine gas coming out our salt shakers." The electrostatic attraction between even two ions is so large that chloride cannot be released in significant amounts. The orange color that they emit is from the excitation of electrons to higher energy levels. They are orange because of impurities in the salt, especially iron oxide (rust). If fire can't make these lamps release negative ions, it's not likely slightly warm electric lights could.
Perhaps these lamps don't ionize the sodium or chlorine in the salt, but the molecules in the air around the lamp. "Negative ions" have been a buzzword used by various woo machines for decades, and there do exist air ionization machines that can indeed negatively ionize air molecules. The only problem is, negatively ionized air molecules don't really cure anything. (If you have a lot of ions in the air, we call it "lightning.") Whether salty air does anything is of course another thing entirely.
Salt Lamps make a good conversation piece and a half-decent night light so you don't step on your cat on your way to the bathroom at 2 AM.
- How Do They Work? Saltlamp.ca, GAMMA Salt Cristals [sic] Ltd.
- Ho-ho Hokum? Los Angeles Times, December 15, 2008, Chris Woolston.
- See lattice energy at Wikipedia. Such values are never directly measured, but determined by thermodynamics. The lattice energy for sodium chloride is 787 kJ/mol.
- Alles nur Kochsalz — LGL nimmt 'Himalayasalz' genauer unter die Lupe (11. August 2003 Nr. 38/03)
- How Salt Works: Table Salt and Sea Salt