Early roentgen electron optical image intensifiers were said to produce an increase in brightness of 500 to 1,000 times when compared with a standard fluoroscopic screen. The light levels were, therefore, of the order of 0.003 cd∕m2 to 3 cd∕m2. Different manufacturers now claim between 1,000 and 6,000 times intensification, but they give very vague information about the screen used for the comparison. Often a Patterson B-2 or CB-2 screen is said to have been employed, but no data are given concerning its age and other parameters. Sometimes special screens have been utilized which are not available on the market. Frequently no mention is made of the radiation quality employed for the measurements. In 1956 the International Commission on Radiological Units (ICRU) formed a Subcommittee to establish standards for measurements of image intensifiers. This Subcommittee finished its work in 1962 and the reports are published in the National Bureau of Standards Handbook 89 (August 1963) (1). It is important to sum...