The sensitivity of an image intensifier tube is measured in microamperes per lumen (μA/lm). It defines how many electrons are produced per quantity of light that falls on the photocathode. This measurement should be made at a specific color temperature, such as "at a colour temperature of 2854 K". The color temperature at which this test is made tends to vary slightly between manufacturers. Additional measurements at specific wavelengths are usually also specified, especially for Gen2 devices, such as at 800 nm and 850 nm (infrared).
