Editing Image intensifier (section)

===MTBF ([[mean time between failure]])===
This value, expressed in hours, gives an idea how long a tube typically should last. It's a reasonably common comparison point, however takes many factors into account. The first is that tubes are constantly degrading. This means that over time, the tube will slowly produce less gain than it did when it was new. When the tube gain reaches 50% of its "new" gain level, the tube is considered to have failed, so primarily this reflects this point in a tube's life.

Additional considerations for the tube lifespan are the environment that the tube is being used in and the general level of illumination present in that environment, including bright moonlight and exposure to both artificial lighting and use during dusk/dawn periods, as exposure to brighter light reduces a tube's life significantly.

Also, a MTBF only includes operational hours. It is considered that turning a tube on or off does not contribute to reducing overall lifespan, so many civilians tend to turn their night vision equipment on only when they need to, to make the most of the tube's life. Military users tend to keep equipment on for longer periods of time, typically, the entire time while it is being used with batteries being the primary concern, not tube life.

Typical examples of tube life are:

First Generation: 1000 hrs<br>
Second Generation: 2000 to 2500 hrs<br>
Third Generation: 10000 to 15000 hrs.

Many recent high-end second-generation tubes now have MTBFs approaching 15,000 operational hours.