Negative ions vs. Filter-type air cleaner – Negative ions cleanse the air by attaching itself to dust, pollen or other particulates which in turn causes these particulates to stick together and fall to the ground, removing them from the air. An air cleaner requires a blower to suck the surrounding air through the filter, while still allowing smaller particles through. The resulting forced output can actually stir up more particulates. With a salt lamp negative ions are naturally generated and can spread throughout a room and purify without the generation of disturbing air flow. The reaction of moisture with the surface of Himalayan salt increases the level of negative ions, which can be released even further with the heat from a bulb. Since Himalayan salt is hygroscopic, the lamp should be left on all of the time in humid areas.