An apparatus for detecting matter, comprisning: - bulk feeding means (3; 3') configured for feeding a plurality of objects (2; 2') into a detecting region; - at least one light source (8; 10, 20; 40) each having a focusing element and being configured to send light in a respective first direction (I 1; I 2) for illuminating at least one object (2; 2') moving in an object plane (P-P) in the detecting region, wherein the at least one light source (8; 10, 20; 40) is a pulsed light source, arranged to send pulsated light (L') into the detecting region; - a first light-analyzing apparatus arranged to sense light that has been emitted from said at least one light source and transmitted through the object, and to identify an amount of light that has been received from said at least one light source after transmission through the object, - means for determining a parameter of the objects based on said identified amount of light received from said at least one light source after transmission through the object wherein said first light-analyzing apparatus is arranged to sense light (TD 1; TD 12) having a direction within the field-of-view of said first light-analyzing apparatus, wherein said respective first direction is different from the directions within the field-of-view of said first light-analyzing apparatus, characterized by; that the first light-analyzing apparatus is further arranged to discriminate between ambient light and said light received from said at least one light source after transmission through the object, - means for switching off said at least one light source for a period of time such that the light-analyzing apparatus measures only the ambient light, and - a processing device arranged to subtract the measured ambient light from the identified amount of light that has been received from said at least one light source after transmission through the object. - bulk feeding means (3; 3') configured for feeding a plurality of objects (2; 2') into a detecting region; - at least one light source (8; 10, 20; 40) each having a focusing element and being configured to send light in a respective first direction (I 1; I 2) for illuminating at least one object (2; 2') moving in an object plane (P-P) in the detecting region, wherein the at least one light source (8; 10, 20; 40) is a pulsed light source, arranged to send pulsated light (L') into the detecting region; - a first light-analyzing apparatus arranged to sense light that has been emitted from said at least one light source and transmitted through the object, and to identify an amount of light that has been received from said at least one light source after transmission through the object, - means for determining a parameter of the objects based on said identified amount of light received from said at least one light source after transmission through the object wherein said first light-analyzing apparatus is arranged to sense light (TD 1; TD 12) having a direction within the field-of-view of said first light-analyzing apparatus, wherein said respective first direction is different from the directions within the field-of-view of said first light-analyzing apparatus, - means for switching off said at least one light source for a period of time such that the light-analyzing apparatus measures only the ambient light, and - a processing device arranged to subtract the measured ambient light from the identified amount of light that has been received from said at least one light source after transmission through the object.