  The detection of atmospheric fluorescence light from extensive air showers
has become a powerful tool for accurate measurements of the energy and mass of
ultra-high energy cosmic ray particles. Employing large area imaging telescopes
with mirror areas of 10m2 or more, showers out to distances of 30km and more
can be observed. Matrices of low-noise photomultipliers are used to detect the
faint light of the air showers against the ambient night-sky background noise.
The signal-to-noise ratio of such a system is found to be proportional to the
square root of the mirror area times the quantum efficiency of the phototube.
Thus, higher quantum efficiencies could potentially improve the quality of the
measurement and/or lead to the construction of more compact telescopes. In this
paper, we shall discuss such improvements to be expected from high quantum
efficiency phototubes that became available on the market only very recently. A
series of simulations has been performed with data of different types of
commercially available high quantum efficiency phototubes. The results suggest
a higher aperture and thus increased statistics for such telescopes.
Additionally, the quality of the reconstruction can be improved.
