Large crystal salt rocks are also used as salt lamps. A salt lamp is a lamp carved from larger salt crystals, often colored, with an incandescent bulb or a candle inside. The lamps give an attractive glow and are suitable for use as nightlights or for ambient mood lighting. Mined in Europe and Asia, when illuminated, salt crystals emit a soft glowing light and are hand-carved. Some believe that heated salt crystals emit negative ions or positive energy waves into the air.