  The Deep Underground Neutrino Experiment (DUNE) is a leading-edge experiment
designed to perform neutrino science and proton decay searches. In particular,
the far detector will consist of four 10-kton Liquid Argon (LAr) Time
Projection Chambers using both single and dual-phase technologies. The latter
provides charge amplification in the gaseous phase. In order to optimize these
designs, two large prototypes are taking data at CERN since 2018. Previously, a
dual-phase 4-tonne demonstrator was constructed and exposed to cosmic muons in
2017 and exhibited good performance in terms of charge and light collection.
The light detection system is important to provide a trigger to the charge
acquisition system and to obtain additional information from the scintillation
light produced in the particle interaction. In the demonstrator, five cryogenic
photo-multipliers were installed with different base polarity configurations
and wavelength shifting methods. During the detector operation, scintillation
light data were collected in different drift and amplification field
conditions. An overview of the light detection system performance and results
on the light production and propagation are presented. Our studies allowed to
improve the understanding of some LAr properties.
