  The simultaneous measurement of phonons and scintillation light induced by
incident particles in a scintillating crystal such as CaWO4 is a powerful
technique for the active rejection of background induced by gamma's and beta's
and even neutrons in direct Dark Matter searches. However, less than ~1% of the
energy deposited in a CaWO4 crystal is detected as light. Thus, very sensitive
light detectors are needed for an efficient event-by-event background
discrimination. Due to the Neganov-Luke effect, the threshold of
low-temperature light detectors based on semiconducting substrates can be
improved significantly by drifting the photon-induced electron-hole pairs in an
applied electric field. We present measurements with low-temperature light
detectors based on this amplification mechanism. The Neganov-Luke effect makes
it possible to improve the signal-to-noise ratio of our light detectors by a
factor of ~9 corresponding to an energy threshold of ~21 eV. We also describe a
method for an absolute energy calibration using a light-emitting diode.
