The present invention relates to a light mixing chamber (100). The light mixing chamber (100) comprising: a first light mixing chamber part (120) comprising a light exit window (122) and a first side wall (124) having a first groove (126); a second light mixing chamber part (140) comprising a bottom wall (142) and a second side wall (144) having a second groove (146); and an LED substrate (160) supporting a plurality of LEDs (162,164,166,168). The LED substrate (160) is arranged into the first (126) and second grooves (146), interconnecting the first and the second light mixing chamber parts (120,140) such that the light mixing chamber (100) is formed. The plurality of LEDs (162,164,166,168) of the LED substrate (160) is facing an inner cavity (180) of the light mixing chamber (100).