An apparatus for inspecting a stream of matter including: a first and a second light source for emitting a first and a second light beam; a first and a second detector; a first scanning element adapted to redirect the detection area of the second detector from side to side across said stream, and a beam splitting element arranged to receive said first and second light beams, after they have been reflected against said matter, wherein said beam splitting element is adapted to guide said reflected first light beam towards said first detector and to guide said reflected second light beam towards said second detector.