This lamp usually a Kamaatchi Amman vilakku . This vilakku is known as "Nilaivilakku". It should be placed on a small tray and kept in the middle facing east (very auspicious). You can keep it on the left of your Istha Deivam. You may keep the vilakku facing north, Never ever placed it facing SOUTH. Do not use ever silver lamp. How to keep our vilakku in the best condition.