  A photomultiplier setup for precise relative CsI(Tl) crystal light yield and
uniformity measurements is described. It is used for wrapping material studies
to optimize the uniformity and the yield of the light output of 36 cm long
crystals. The uniformity is an important property in high energy photon
calorimetry. Results of an optimization of photodiode coupling to crystals, the
influence of temperature and radiation damage to light and photoelectron yield
are also presented.
