The present invention relates to a light source (100) comprising a substrate (110) having a slit (112) and a sheet formed heat sink structure (120) comprising a plurality of LEDs (130), wherein the plurality of LEDs are arranged at a surface (122) of the heat sink structure and wherein the heat sink structure is mounted through the slit such that a LED comprising portion (124) of the heat sink structure, extending from a first side (114) of the 5 substrate, and a heat-emitting portion (126) of the heat sink structure, extending from a second side (116) of the substrate being opposite to the first side, are formed. A lighting system comprising such a light source is also presented.