Use a 15-watt light bulb for small salt lamps, a 25-watt bulb for medium and large lamps and a 40-watt bulb for very large lamps, depending on your salt rock light manufacturer. The different wattage provides the heat required to release the negative ions for each lamp size. The heat should not burn your hand, but should feel warm when you touch it.
Keep your salt rock lights turned on 24 hours each day, so the light bulb inside of your lamp can keep the lamp heated in order to generate negative ions. Leaving your lamp on at all times also heats the salt crystal, evaporating any moisture that may build up.
Remove white powder carefully from the surface of your salt rock lamp with a soft, damp cloth while you have your lamp turned on. This white powder forms in the presence of excess humidity in the room, such as that from a bathroom, as the salt crystals in your lamp quickly dissolve. Salt naturally attracts moisture from the air and the white powder comes from the interaction of the salt crystals and water molecules. Avoid exposing your salt rock lamp to humidity levels higher than 60 percent.
Wrap a bag made of polythene, a waxy flexible plastic, over your salt rock lamp to protect it from humidity if you know you will not be using your lamp for a long time but still want to display it.