  The Deep Underground Neutrino Experiment (DUNE) is a 40-kton underground
liquid argon time-projection-chamber (LAr TPC) detector, for long-baseline
neutrino oscillation studies and for neutrino astrophysics and nucleon decay
searches. Photon detector systems embedded within the LAr TPC add precise
timing capabilities for non-beam events. The ProtoDUNE dual phase detector will
consist of a 6x6x6 m3 liquid argon time-projection chamber placed at CERN and
the light readout will be formed by 8-inch cryogenic photomultipliers from
Hamamatsu. The characterization of the 36 photomultipliers, the base design,
and the light calibration system are described. In addition, preliminary
results from a 3x1x1 m3 LAr double phase detector operating at CERN are
presented.
