LEDs are cooled either by passive cooling or active cooling. Passive cooling involves a finned heat exchange system made of cast or extruded metal or plastic coated metal heat sink that offers a totally silent, robust, heat transfer. Passive cooling is reliant on the surface area of heat sink material and is orientation dependant. Active cooling may include conventional fans or diaphragm- based forced air cooling. Active cooling using a fan, although more efficient; is noisy, not so reliable, and needs electricity to run. Active cooling lays emphasis on forced air flow rate and is not orientation dependant.