An additional U(1) symmetry predicted in theories beyond the Standard Model of
particle physics can give rise to hidden (dark) photons. Depending on the mass
and density of these hidden photons, they could account for a large fraction of
the Dark Matter observed in the Universe. When passing through an interface of
materials with different dielectric properties, hidden photons are expected to
produce a tiny flux of photons. The wavelength of these photons is directly
related to the mass of the hidden photons. In this contribution we report on
measurements covering the visible and near-UV spectrum, corresponding to a dark
photon mass in the eV range. The data were taken with the FUNK experiment
using a spherical mirror of $\sim$ 14 m$^2$ total area built up of 36
aluminum segments.