Large-mass arrays of bolometers proved to be good detectors for neutrinoless double beta decay (0νDBD) and dark matter searches. CUORE and LUCIFER are bolometric 0νDBD experiments that will start to take data in 2015 at Laboratori Nazionali del Gran Sasso in Italy. The sensitivity of CUORE could be increased by removing the background due to α particles, by detecting the small amount of Čerenkov light (∼100 eV) emitted by the βs' signal and not by αs. LUCIFER could be extended to detect also dark matter, provided that the background from β/γ particles (∼ 100 eV of scintillation light) is discriminated from nuclear recoils of about 10 keV energy (no light). We have recently started to develop light detectors for CUORE, LUCIFER and similar bolometric experiments. The aim is to obtain detectors with an active area of 5×5 cm2 (the face of bolometric crystals), operating at 10 mK, and with an energy resolution at the baseline below 20 eV RMS. We have chosen to develop phonon-mediated detectors with KID sensors. We are currently testing the first prototypes. © 2014 Springer Science+Business Media New York.