Disclosed is a device for detecting at least one luminescent substance, comprising a radiation source for emitting excitation radiation to the at least one luminescent substance. The excitation radiation is provided with at least one excitation wavelength at which the luminescent substance is excited so as to emit luminescent radiation. At least one radiation receiver is provided, which detects the luminescent radiation and is configured regarding the spectral sensitivity thereof in such a way that said radiation receiver is insensitive to the radiation emitted by the radiation source. The luminescent substance is located inside a measuring chamber that is essentially impermeable to the luminescent radiation and comprises at least one wall area which is transparent to the excitation radiation emitted by the radiation source. The radiation source is placed outside the measuring chamber such that the excitation radiation emitted by the radiation source is coupled into the inside of the measuring chamber by penetrating said wall area.