A summary is given of measurements of the photoelectron counting efficiency of a variety of image intensifiers manufactured by several different manufacturers. With one exception, the counting efficiency is disappointingly low. Typically only slightly over half of the photoelectrons from the first photocathode produce a detectable signal on the output phosphor screen in most diode-type intensifiers. For microchannel plate intensifiers, the counting efficiency is even less. Results are given of experiments intended to produce diode-type intensifiers having improved counting efficiency. Improvements have been achieved through refinements in the manufacturing steps of the phosphor screen, the tube component identified as responsible for the lost photoelectron pulses in diode-type tubes. The best tubes so far have counting efficiencies of 70%, which represent an improvement by a factor of about 1.4.