The Gen. 1 Night vision devices were introduced in the Vietnam war and were the first passive night vision devices that could operate with the ambient light. Such devices could amplify the light up to 1000 times, but for a brighter picture, an artificial infrared light still was needed. Improved versions of Gen. 1 NV devices still are available today, but also those need an infrared illuminator in darker areas.
Yukon NV Binoculars
Generation 1 devices have a clear picture in the middle, but mostly they are blurry on the edges. These devices are known because when you turn the device on and later off, you still have a green picture when you turn the device off. The image then slowly gets darker until it completely turns off. This is because the electrons are still electrically charged and they slowly discharge.
The useful range for Gen. 1 devices is normally up to 50-75 meters, and recommended is the use under the moonlight. For darker areas, an infrared illuminator is needed, but thankfully almost all devices have one integrated. These devices operate in a spectrum of up to 800nm.
Be careful that you don't open the cover of your night vision at day because this could quickly damage your image-intensifier tube!