  The next generation of bolometric experiments searching for rave events, in
particular for the neutrino-less double beta decay, needs fast,
high-sensitivity and easy-to-scale cryogenic light detectors. The CALDER
project (2014-2020) developed a new technology for light detection at cryogenic
temperature. In this paper we describe the achievements and the final prototype
of this project, consisting of a $5\times5$ cm$^2$, 650 $\mu$m thick silicon
substrate coupled to a single kinetic inductance detector made of a three-layer
aluminum-titanium-aluminum. The baseline energy resolution is
34$\pm$1(stat)$\pm$2(syst) eV RMS and the response time is 120 $\mu$s. These
features, along with the natural multiplexing capability of kinetic inductance
detectors, meet the requirements of future large-scale experiments.
