Editing Image intensifier (section)

===Gain===
The gain of a tube is typically measured using one of two units. The most common (SI) unit is cd·m<sup>−2</sup>·lx<sup>−1</sup>, i.e. [[candelas]] per meter squared per [[lux]]. The older convention is Fl/Fc ([[foot-lambert]]s per [[foot-candle]]). This creates issues with comparative gain measurements since neither is a pure ratio, although both are measured as a value of output intensity over input intensity. This creates ambiguity in the marketing of night vision devices as the difference between the two measurements is effectively [[pi]] or approximately 3.142x. This means that a gain of 10,000&nbsp;cd/m<sup>2</sup>/lx is the same as 31.42 Fl/Fc.