Device (100, 500) for sensing and determining an amount of mold on building-material surfaces (101, 501) in the field, said mold being fluorescent when irradiated with ultraviolet light (104, 504), comprising: a first light source (103, 503) configured to radiate ultraviolet light (104, 504) onto an area to be examined (102, 502) of the building-material surface (101, 501), a second light source configured to emit light within a wavelength range that is different as compared to that of the first light source (103, 503) and to radiate same onto that area to be examined (102, 502) of the building-material surface (101, 501), both light sources (503, 512) being sequentially switchable, a light receiver (105, 505) configured to receive light (106, 506) from the area to be examined (102, 502) so as to take pictures of the area to be examined (102, 502) in different illumination scenarios, a control unit (107, 507) configured to compare a picture taken of the area to be examined (102, 502) that is illuminated with the first light source to a picture taken of the area to be examined (102, 502) which is illuminated with the second light source, so as to inspect the light (106, 506) received by means of the light receiver (105, 505) in terms of whether the light (106, 506) received comprises light that has fluoresced at least in portions so as to at least qualitatively determine the presence of mold, and wherein the control unit (107, 507) is further configured to quantitatively determine, in the event that a fluorescent portion of light has been identified, the amount of mold present on at least part of the building-material surface (101, 501) on the basis of qualitative sensing of mold that was previously performed in at least an area to be examined (102, 502) of the building-material surface (101, 501). a first light source (103, 503) configured to radiate ultraviolet light (104, 504) onto an area to be examined (102, 502) of the building-material surface (101, 501), a second light source configured to emit light within a wavelength range that is different as compared to that of the first light source (103, 503) and to radiate same onto that area to be examined (102, 502) of the building-material surface (101, 501), both light sources (503, 512) being sequentially switchable, a light receiver (105, 505) configured to receive light (106, 506) from the area to be examined (102, 502) so as to take pictures of the area to be examined (102, 502) in different illumination scenarios, a control unit (107, 507) configured to compare a picture taken of the area to be examined (102, 502) that is illuminated with the first light source to a picture taken of the area to be examined (102, 502) which is illuminated with the second light source, so as to inspect the light (106, 506) received by means of the light receiver (105, 505) in terms of whether the light (106, 506) received comprises light that has fluoresced at least in portions so as to at least qualitatively determine the presence of mold, and wherein the control unit (107, 507) is further configured to quantitatively determine, in the event that a fluorescent portion of light has been identified, the amount of mold present on at least part of the building-material surface (101, 501) on the basis of qualitative sensing of mold that was previously performed in at least an area to be examined (102, 502) of the building-material surface (101, 501).