An I.R. illuminator is a device that, like a flashlight, emits infrared light. On the other hand, infrared light is nearly undetectable to the naked eye but quite noticeable to night vision equipment. Infrared illumination is incorporated into all Gen 1 equipment and is always on. This is because, without the I.R. light, you would see very little with Generation 1 items. Because Gen 2 and Gen 3 gear has over 1000 times the light amplification of Gen 1, an always-on I.R. illuminator is no longer required. Gen 2 and above equipment with built-in illuminators have on/off switches for their illuminators; however, Gen 1 equipment does not have an on/off switch because the illumination is constantly on. You won't always need an infrared illuminator with high-quality equipment, but it can quadruple the capability of your device and allow you to see things that would be hard to see without one.