We measured the attenuation losses and the corresponding number of photoelectrons in small diameter fibre bundles. Accordingly, two experimental setups have been developed for this purpose. The improvements in light yield of the last two years, due to better fibre production and to optimization of materials, concentrations and geometrical characteristics, are shown and discussed in detail. For 60 mum diameter fibre bundle, they amount to a factor 2 at the near end and to a factor 8 at 2 m distance from the light detecting photocathode.