The important performance parameters are:

• Signal-to-Noise Ratio (SNR)
• Resolution and MTF
• Lifetime

Signal-to-noise ratio:
This is by far the most important parameter for an Image Intensifier. It is a measure of the light signal reaching the eye divided by the perceived noise as seen by the eye. For Night Vision devices it is measured at a light-level of 108 ulx.

The value of the SNR determines the resolution at very low light-levels. Therefore, the higher the SNR the better the ability to resolve image details under low light-level conditions. The SNR is related to the specific design of the tubes.

Low signal-to-noise ratio	High signal-to-noise ratio

Resolution and Modulation Transfer Function (MTF)
Resolution is the maximum line density on a USAF target that can be resolved by a human eye and is expressed in line pairs per mm (lp/mm). A more objective performance indicator is given by the Modulation Transfer Function (MTF). High MTF values at low spatial frequencies provide - like for the XD-4™ tubes - sharp images with a good contrast.

Lifetime
The life time of an Image Intensifier is an extremely important parameter for Night Vision applications. A number of different definitions are used depending on the manufacturer. For the XD-4™ Image Intensifiers of PHOTONIS the life time of 15000 hours is the expected life time, which is defined as the time after which still 50 % of the original sensitivity is left.