  ATLAS is a general purpose experiment approved for the LHC collider at CERN.
An important component of the detector is the central hadronic calorimeter; for
its construction more than 600,000 Wave Length Shifting (WLS) fibres
(corresponding to a total length of 1,120 Km) have been used.
  We have built and put into operation a dedicated instrument for the
measurement of light yield and attenuation length over groups of 20 fibres at a
time.
  The overall accuracy achieved in the measurement of light yield
  (attenuation length) is 1.5% (3%).
  We also report the results obtained using this method in the quality control
of a large sample of fibres.
