  The ANAIS experiment aims at the confirmation of the DAMA/LIBRA signal using
the same target and technique at the Canfranc Underground Laboratory (LSC) in
Spain. ANAIS detectors consist of large NaI crystals coupled to two
photomultipliers (PMTs). In this work we present Single Electron Response (SER)
data for several units of the Hamamatsu R12669SEL2 PMT model extracted from
normal operation data of ANAIS underground prototypes and we compare them with
PMT SER characterization previously done at surface lab before coupling them to
NaI crystal. Moreover, total light collection for different ANAIS prototypes
has been calculated, producing an excellent average result of 15 phe/keV, which
has a good impact in both energy resolution and threshold.
