  A novel light detection scheme has been tested for use in medium-pressure gas
TPCs, in view of rare events searches in low energy particle physics. It has
the advantage of minimal interference with the ionization collection system,
used for track imaging. It provides an absolute time reference, which allows an
absolute determination of the Z coordinate of events, along the direction of
the drift field. This makes possible a fiducial cut along the Z-axis, allowing
to reduce the background from the ends of the drift volume.
