Since 1960s, the technological progress of low light level night vision technology has always been evaluated by "generation". According to usual understanding, the second generation is better than the first generation, and the third generation is superior to the second generation. In 20th century, during the developments of image intensifiers for low light level night vision (LLLNV), the first generation fiber optical cascade coupled image intensifier in 1960s, the second generation image intensifier with microchannel plate (MCP) in 1970s, the third generation image intensifier with GaAs negative electron affinity (NEA) photocathode in 1980s, appeared one and another. The new generation image intensifier or the fourth generation image intensifier has been continuously explored by scientists engaged in night vision technology. But, for the image intensifiers, what is the fourth generation, what can be called the fourth generation, it has some arguments in the night vision academic circle. The problems are as the following : whether or not it is appropriate and comprehensive for the image intensifiers to be divided by“generation”and evaluated also by“generation”;what is exactly when we evaluate an image intensifier by useof the performance or the technology ;and what is better and more comprehensive for expressing the performance of an image intensifier. All these problems have been paid attention by night vision academic circle. The present paper shows that the overall performance of low light level image intensifiers should be evaluated by the“figure of merit”, rather than by the concept of“generation”.