An LED assembly includes a heat sink and a plurality of LED modules attached to the heat sink. The heat sink includes a heat conducting body and a plurality of fins extending from the heat conducting body. The heat conducting body has a middle flat portion and two sloped portions at two sides of the middle fat portion. Each sloped portion has a plurality of steps descending from the middle portion. The LED modules are thermally attached to the heat conducting body. Some of the LED modules are mounted on the middle flat portion and others are mounted on the steps of the sloped portions of the heat conducting body of the heat sink. The fins have distal ends cooperatively define a flat plane for the heat sink.