  The peak photon detection efficiency (PDE) of silicon photomultipliers
(SiPMs) can be as good or better than the PDE of photomultiplier tubes (PMTs).
There are experiments where the signal is measured in the presence of a strong,
steady background light emission. In these, one needs to accurately evaluate
the signal-to-noise ratio. Imaging Atmospheric Cherenkov Telescopes (IACTs)
observe in the presence of strong noise induced by the light of the night sky.
It is certainly interesting to investigate the SiPM performance under
operational conditions of IACTs and to compare it with that of the PMTs. For
that purpose, we built a SiPM-based detector module, which was installed in one
of the imaging cameras of the two Major Atmospheric Gamma-ray Imaging Cherenkov
(MAGIC) telescopes in 2015. The experience gained from that module was used to
design the second generation of modules of improved performance. Two such
modules were installed in 2017. MAGIC is a system of two IACTs located on the
Canary Island of La Palma. The mechanical structure of the MAGIC imaging
cameras offers the possibility to install up to 6 additional detector modules
of 7 pixels each into the open vertices of the hexagonal-shaped camera. This
allows us to directly, without making any assumption, compare the performance
of the PMT-based modules with that of the SiPM-based prototype modules, where
SiPMs from three different manufacturers are used.
