Radiance amplification has been demonstrated in a two‐stage fluorescence radiation converter consisting of fluorescent acrylic glasses and suitably attached reflectors. The experimental results are in agreement with the theory for such systems. Internal absorption of the fluorescence radiation reduces the radiance amplification considerably. Fluorescence converter systems seem to offer some advantages in the detection of diffuse, nondirectional quantum and particle radiation and for the application of small semiconductor detectors with high sensitivity in the long‐wavelength region of the visible spectrum.