Substrates and packages for LED-based light devices can significantly improve thermal performance and provide separate electrical and thermal paths through the substrate. One substrate includes multiple electrically insulating base layers. On a top one of these layers are disposed top-side electrical contacts, including light device pads to accommodate a plurality of light devices. External electrical contacts are disposed on an exterior surface of the substrate. Electrical paths connect the top-side electrical contacts to the external electrical contacts. At least portions of some of the electrical paths are disposed between the electrically insulating base layers. The electrical paths can be arranged such that different subsets of the light device pads are addressable independently of each other. A heat dissipation plate can be formed on the bottom surface of a bottom one of the base layers.