cnoct posts on a night vision forum as stanley. The gen2 vs gen3 debate has been going on over there for many years. I don't know if it is ok to post links to another forum, so I will post an excerpt from one of stanley's 2011 posts. If you are any good at all with google this should provide a trailshead to get you more information. If either cnoct or the mods do not think this post is appropriate, just let me know and I will promptly delete it.
posted by stanley
Here are some important difference between all gen 2 (+ or not) and all gen III tubes. The main differences between them, is the wavelength ranges they are sensitive to.
Gen 2 tubes use a multialkalai photocathode and have their peak sensitivity in the visible range, with the range of most useful sensitivity from 400 to 600 nm. The total range of sensitivity is limited at short wavelengths by the glass envelop at about 325nm. On the long wavelength end the sensitivity trails off to about half of peak by 700 nm reaching zero useful sensitivity at about 1000nm.
Gen 3 tubes use a Gallium Arsenide photocathode. They generally have their greatest sensitivity in the 700 to 900nm range. GaAs is also inherently limited at the short end by the glass envelope, but many tubes are manufactured which purposely suppress the sensitivity in the visible range to improve the ability to see through haze in moonlight. For those tubes the useful range is from around 550 nm to 950 nm where GaAs cuts off sharply. There are some Gen3‘s doped to give response to 1100nm, but they are noisier than other tubes and don’t give better dark performance. They are used when being able to use light from YAG lasers at 1064nm is required.
Whether a G2+ or G3 tube will give better apparent performance depends more on the illumination present and the tube construction. In either tube, the resolution is determined by the following, not the photocathode material:
1) input faceplate material
2) micro channel plate
3) focusing distance between components
4) thickness and particle size of the phosphor material
Gen 2+ will give better performance when the illumination comes primarily from sources, which have mostly visible energy. Such sources include dawn and dusk sky glow, moonlight, (which is just reflected sunlight) and light from local artificial sources like residential or highway lighting and distant towns or cities. In some parts of the world, like most of Europe, Japan, and most of the coastal regions along the eastern seaboard of U.S. In the aforementioned location, you can‘t get away from artificial light as the primary illumination source.
On moonless nights in rural or ocean areas of the world the situation changes. The primary source of illumination is from sky glow resulting from high velocity solar particles striking the upper atmosphere. That is the primary source of sky brightness on moonless night. It is several times brighter in the 700-1000 nm infrared range than the sum off all visible starlight and sky glow. . For that Gen 3 makes the most efficient use and in those conditions gen 3 tubes (regardless of resolution) will have better sensitivity and signal/noise than gen 2+. That‘s why they‘re used extensively in aviator goggles and by the US military, which can‘t count on artificial illumination being available.
So which is better? That depends on where you are and the available illumination. Hence, it‘s not a question of one being better than the other, only more suitable.