Salt crystal lamps emit negative ions into the surrounding atmosphere, which work to neutralize and improve air quality. The salt absorbs water molecules from the air, and releases them when lit. The larger the lamp and the warmer the light, the more negative ions are released into the air.
When inhaled, negative ions create biochemical reactions in the brain that increase serotonin levels, bringing a sense of peace and tranquillity. Higher levels of negative ions are found around waterfalls, on beaches and even in a household shower. The presence of negative ions has a greater effect on some people than on others.
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.