Packages for LED-based light devices include interface structures that can facilitate heat transfer from the package to a heat sink. The package can include multiple LEDs mounted on a ceramic substrate that provides electrically conductive pathways between the LEDs and metal contact pads at a peripheral region of a top surface of the substrate. A bottom surface of the substrate can be patterned with a plate, such as a thick supporting plate, made of metal and/or other materials with high thermal conductivity, that can be attached to an external heat sink.