Method for detecting the interior volumes of nonblocked hollow fibers that are constituents of a bundle (B1, B2) of hollow fibers, wherein - the bundle (B1, B2) comprises a front surface (SF1, SF2) and a rear surface (HF1, HF2), - the hollow fibers are comprised of a first material, in particular a synthetic material, such as for example polysulfone or another polymer, and extend from the front surface (SF1, SF2) to at least the rear surface (HF1, HF2) of the bundle (B1, B2), - the front surface (SF1, SF2) is jointly formed by the front-face edge faces of the hollow fibers and the front-face surface of a binding substance, which - is also a constituent of the bundle (B1, B2) and is comprised of a second material, in particular a synthetic material such as, for example, polyurethane resin or polyurethane, - is located in the region between the front surface (SF1, SF2) and the rear surface (HF1, HF2) between the hollow fibers - and in which the hollow fibers are at least in this region embedded, - and the front-face surface of the binding substance is of such glossiness that the binding substance reflects check light irradiated onto the front surface (SF1, SF2) at least partially specularly and at most partially diffusely, characterized by the following steps: d) the front surface (SF1, SF2) is illuminated by means of a check light (PQ1, PQ2), comprised of a single check light source or a plurality of single check light sources, which radiates or radiate its/their light omnidirectionally into a half-space below the check light source, and wherein as the check light source (PQ1, PQ2) a planarly extended light source (PQ1, PQ2) is employed which, viewed from each point of the front surface (SF1, SF2), span in their totality an envelope that appears amidst an aperture angle (alpha) of at least 60° or at least 35° or at least 30° and generates check light (PL1, PL2, PL3), e) by means of a check camera, check light (PL1, PL2, PL3) is recorded after it has been specularly reflected at the front-face surface of the binding substance and in this manner, by means of the check camera, a specular light image (GLB1, GLB2) of the front surface (SF1, SF2) is generated in which the interior volumes of nonblocked fibers appear darker than the front-face surface of the binding substance as well as in particular also darker than the interior volumes of such hollow fibers that in the proximity of the front surface (SF1, SF2) are blocked by binding substance, f) the images (H') of the interior volumes of nonblocked hollow fibers are automatically detected based on this darkening in the specular light image (GLB1, GLB2), by means of image processing or they are detected and counted. - the bundle (B1, B2) comprises a front surface (SF1, SF2) and a rear surface (HF1, HF2), - the hollow fibers are comprised of a first material, in particular a synthetic material, such as for example polysulfone or another polymer, and extend from the front surface (SF1, SF2) to at least the rear surface (HF1, HF2) of the bundle (B1, B2), - the front surface (SF1, SF2) is jointly formed by the front-face edge faces of the hollow fibers and the front-face surface of a binding substance, which - is also a constituent of the bundle (B1, B2) and is comprised of a second material, in particular a synthetic material such as, for example, polyurethane resin or polyurethane, - is located in the region between the front surface (SF1, SF2) and the rear surface (HF1, HF2) between the hollow fibers - and in which the hollow fibers are at least in this region embedded, - and the front-face surface of the binding substance is of such glossiness that the binding substance reflects check light irradiated onto the front surface (SF1, SF2) at least partially specularly and at most partially diffusely, d) the front surface (SF1, SF2) is illuminated by means of a check light (PQ1, PQ2), comprised of a single check light source or a plurality of single check light sources, which radiates or radiate its/their light omnidirectionally into a half-space below the check light source, and wherein as the check light source (PQ1, PQ2) a planarly extended light source (PQ1, PQ2) is employed which, viewed from each point of the front surface (SF1, SF2), span in their totality an envelope that appears amidst an aperture angle (alpha) of at least 60° or at least 35° or at least 30° and generates check light (PL1, PL2, PL3), e) by means of a check camera, check light (PL1, PL2, PL3) is recorded after it has been specularly reflected at the front-face surface of the binding substance and in this manner, by means of the check camera, a specular light image (GLB1, GLB2) of the front surface (SF1, SF2) is generated in which the interior volumes of nonblocked fibers appear darker than the front-face surface of the binding substance as well as in particular also darker than the interior volumes of such hollow fibers that in the proximity of the front surface (SF1, SF2) are blocked by binding substance, f) the images (H') of the interior volumes of nonblocked hollow fibers are automatically detected based on this darkening in the specular light image (GLB1, GLB2), by means of image processing or they are detected and counted.