A mounting substrate for a semiconductor light emitting device comprising: a solid aluminium block including a cavity in a first face thereof, that is configured for mounting a semiconductor light emitting device therein, the cavity including a cavity floor and an oblique cavity sidewall that surrounds the cavity floor; an electrically insulating coating on the first face of the solid aluminium block and extending into the cavity, including onto the cavity sidewall and onto the cavity floor; and first and second spaced apart electrically conductive traces (130a", 130b") on the insulating coating, the first and second conductive traces extending from the first face onto the cavity sidewall and onto the cavity floor for connection to a semiconductor light emitting device, at least a portion (132a, 132b) of the first and second spaced apart conductive traces in the cavity comprising a reflecting material for reflecting light that is emitted by a semiconductor light emitting device in the cavity; wherein the solid aluminium block includes therein first and second through holes (140a', 140b') that extend from the first face, outside the cavity, to the second face of the solid metal block that is opposite the first face, the respective first and second through holes including an electrically insulating coating thereon and a respective first and second conductive via (142a', 142b') therein that extend from the first face outside the cavity to the second face and wherein a respective one of the first and second spaced apart conductive traces is electrically connected to a respective one of the first and second conductive vias. a solid aluminium block including a cavity in a first face thereof, that is configured for mounting a semiconductor light emitting device therein, the cavity including a cavity floor and an oblique cavity sidewall that surrounds the cavity floor; an electrically insulating coating on the first face of the solid aluminium block and extending into the cavity, including onto the cavity sidewall and onto the cavity floor; and first and second spaced apart electrically conductive traces (130a", 130b") on the insulating coating, the first and second conductive traces extending from the first face onto the cavity sidewall and onto the cavity floor for connection to a semiconductor light emitting device, at least a portion (132a, 132b) of the first and second spaced apart conductive traces in the cavity comprising a reflecting material for reflecting light that is emitted by a semiconductor light emitting device in the cavity; wherein the solid aluminium block includes therein first and second through holes (140a', 140b') that extend from the first face, outside the cavity, to the second face of the solid metal block that is opposite the first face, the respective first and second through holes including an electrically insulating coating thereon and a respective first and second conductive via (142a', 142b') therein that extend from the first face outside the cavity to the second face and wherein a respective one of the first and second spaced apart conductive traces is electrically connected to a respective one of the first and second conductive vias.