Gain is an information, that tells you the number of times a night vision amplifies the ambient light. The image intensifier is the heart of all analog night vision devices and it is the main component. Effectivity of the intensifier is measured with “gain”. The older Gen 1 night vision devices have a GAIN from 500 – 2000 times. The gain for Gen 2 NV devices is typically from 10.000 – 20.000 times, and there are Gen 2 NV devices with different photocathode options on the market that even exceeds those values. Gen 2 with higher quality photocathode falls into Gen 2+ night vision category, which GAIN value is 25.000 to even 45.000 with the newest photocathode Photonis XR-5. The gain on Gen 3 NV devices is from 40.000 to 65.000 times.
The bigger the gain, the bigger amplification of the ambient light, the brighter and better quality image you will get and of course, the higher the price.