According to About.com Holistic Healing, salt lamps work by emitting negatively charged ions into the air. When the salt lamp is heated, either by a candle or a light bulb, the heat draws moisture out of the air and through the salt. This process emits various levels of negatively charged ions depending on the size of the lamp and how hot it gets.
Negative charged ions have an assortment of benefits that include increasing chi, decreasing allergens in the air, reducing seasonal affective disorder, increasing serotonin levels and boosting the immune system. Salt lamps are most commonly made out of Himalayan rock salt, or halite, which is imported from Pakistan.
According to the Himalayan Salt Shop, salt lamps can come in sizes between 4 and 50 pounds, and they typically emit a reddish hue when lit. There are white salt crystal lamps, but these are very rare. The reddish coloring is characteristic of Himalayan rock salt, and it is due to iron oxide that is found in the crystal. Wikipedia states that in addition to iron oxide, the salt that makes up salt lamps is composed of 95 to 96 percent sodium chloride and 2 to 3 percent polyhalite. The salt also contains trace amounts of ten other minerals.
Red salt lamps are said to promote circulation and activate the heart, while orange colored lamps help the nervous system. Lamps with pink coloring stimulate love, and white lamps offer healing, cleansing and detoxification.