March 25, 2025

Understanding Night Vision Parameters

Let’s talk about specifications of Gen 2 Image Intensifier tubes that will help you better understand Night Vision technology.

The heart of every night vision device is its Image IntensifierTube (often referred to as IIT). It might be very confusing for a beginner to understand and decipher different tube parameters.

The most common parameter is image resolution. It refers to image clarity and sharpness. Image tubes with high resolution will provide crisp image with more details and will perform even better when used with higher optical magnification. Image resolution is measured in lp/mm which stands for lines per millimetre. The higher this value is the sharper image you will get.

Signal-to- Noise Ratio (often referred to as SNR) is a value that helps you to understand how good the tube will perform in difficult low-light conditions. We all tried taking pictures at night time and couldn’t help but notice that the image quality is usually worse. Image gets a bit grainy and noisy. It’s similar with Night Vision. The less light there is to amplify the noisier the image will get. To put it in simple words the image becomes darker and starts “snowing” a bit. SNR doesn’t have a measurement unit of its own, but the general idea is that higher value results in less noise you will see in the image.

To make it even easier for an average user to assess the IIT quality, night vision manufacturers came up with a generalized parameter for that - Figure of Merit (often referred to as FOM). It’s a combination of 2 parameters we discussed previously. FOM is calculated through multiplying Image resolution by Signal-to-Noise Ratio. This figure will give you a basic estimation about the tube parameters. Higher FOM value means better tube parameters.

Some tubes have special functions like manual gain control (often referred to as MG or EGAC). It allows the night vision user to regulate tube’s light sensitivity manually. This means that if some light sources are present in field of view, one can dim the tube manually to adapt to new light conditions.

Another particular function would be Autogating. Autogated tubes will give you advantage in changing light conditions by super fast adaptation of its light sensitivity to optimize image quality and provide certain protection from bright light exposure.