A Night Vision Device can be either a 1st, 2nd, 3rd or 4th generation unit. What this stands for is what type of light intensifier tube is used for that particular device The light intensifier tube is the heart and soul of an NVD.
1st generation is currently the most popular type of night vision in the world. Utilizing the basic principles described earlier, a 1st generation will amplify the existing light several thousand times letting you clearly see in the dark. These units provide a bright and sharp image at a low cost, which is perfect, whether you are boating, observing wildlife, or providing security for your home.
2nd generation is primarily used by law enforcement or for professional applications. The main difference between a 1st and a 2nd generation unit is the addition of a micro-channel plate, commonly referred to as a MCP. The MCP works as an electron amplifier and is placed directly behind the photocathode. The MCP consists of millions of short parallel glass tubes. When the electrons pass through these short tubes, thousands more electrons are released. This extra process allows 2nd generation units to amplify the light many more times then 1st generation giving you a brighter and sharper image.
3rd generation By adding a sensitive chemical, gallium arsenide to the photocathode a brighter and sharper image was achieved over 2nd generation. An ion barrier film was also added to increase tube life. Gen. 3 provides the user with good to excellent low light performance.
4th Generation / Gated Filmless tubes:
4th generation / Gated Filmless technology represents the biggest technological breakthrough in image intensification of the past 10 years. By removing the ion barrier film and "Gating" the system Gen 4 demonstrates substantial increases in target detection range and resolution, particularly at extremely low light levels.
Here you can see Night Vision Scenes taken by Night Vision devices of various generations: ...