Glossary

GEN 1: 1st generation is currently the most widespread and popular due to their low cost and utility.   They provide a bright sharp image and amplify light effectively, but you may see some slight blurring around the edges due to geometric distortion, and the unit may glow green after you have switched it off.  Users have also complained about a high pitch hum that comes from the unit, but these conditions which are normal for first generation units, and work great in everyday applications, though they require moonlight to function properly. Light amplification is around 10000x

GEN 2:Second generation night vision scopes possess the micro channel plate (MCP) with a multi-alkali coating to increase the photoelectric properties.  Releasing electrons more readily improves the brightness output on the phosphor screen especially around the edges of the lens. Light amplification is around 20000x.

Later advancements in GEN 2 technology has brought tactical characteristics of GEN 2+ devices.

GEN 3: Third generation night vision systems maintain the MCP from Gen 2, but now use a photocathode made with gallium arsenide, which further improves image resolution. In addition, the MCP is coated with an ion barrier film for increased tube life. The light amplification is also improved to around 30000-50000x.

GEN 4: The unofficial name for the 4th generation of night vision device technology. The advancement comes with an automatic gated power supply that regulates the photocathode voltage so that the night vision scope can adapt instantly to changing light conditions. The second improvement is the thinning or removing of an ion barrier which increases the amount of electrons that are passed through the MCP, resulting in less noise and higher noise sensitivity.
The United States military describes these systems as Generation 3 Autogated tubes (GEN-III OMNI-VII).