The COUNTblue series single-photon-counting modules manufactured by Laser Components GmbH achieve a quantum efficiency of 60% in the blue spectral range and 70% in the yellow and green wavelengths. The heart of the series is a blue-enhanced silicon Geiger-mode low-noise avalanche photodiode that, together with optimized electronics, produces dark count rates of 10 to 250 counts per second. The modules are suitable for use in fluorescence measurement. They are available with an FC connection for optical fibers with a core diameter of up to 105 μm, or in a free-beam version. They are plug-and-play-compatible with standard photon counters available on the market.