Understanding the FOM of NNVT Night Vision Tubes
Understanding the FOM of NNVT night vision tubes
When comparing night vision tubes, one figure comes up time and again: FOM, often displayed as "1200+," "1800+," or "2300+." It is the most decisive factor for image quality—far more so than the tube generation alone. Yet, it remains widely misunderstood. This guide explains what FOM actually is, how it is calculated, and, above all, how to choose the right level for your specific needs.
What is the FOM?
FOM stands for Figure of Merit. It is a single value that summarizes the overall optical performance of a light intensifier tube. It is calculated by multiplying two measurements taken during the quality control of the tube:
FOM = Resolution (lp/mm) × Signal-to-Noise Ratio (SNR)
- Resolution, expressed in line pairs per millimeter (lp/mm), measures the fineness of detail the tube can reproduce. The higher the value, the sharper the image.
- The signal-to-noise ratio (SNR) measures the tube's ability to produce a clean image rather than a grainy one ("scintillation noise"), especially in very low light.
A tube can have excellent resolution but a low SNR, and vice versa. The FOM allows tubes to be compared using a single figure that combines both, making it the most reliable benchmark for assessing a tube's true quality—far more so than the generation (Gen 2+, Gen 3), which on its own reveals nothing about the manufacturing quality of a specific unit.
Why do two tubes of the same generation have a different FOM?
Even when coming off the same production line, two tubes of the same generation can have vastly different FOM ratings. The manufacturing process is inherently variable: each tube is tested individually and then graded based on its measured performance. This is why high-FOM tubes (2000+, 2300+) are rarer and more expensive—they represent the top tier of quality from a single production line.
At NNVT (JPNV), every tube comes with a manufacturer's test sheet indicating its actual FOM, resolution, and measured SNR—not an estimate, but a certified value.
Available FOM tiers
| FOM | Typical use | What this changes in practical terms |
|---|---|---|
| 1200+ – 1400+ | Discovery, occasional use, controlled budget | Decent image quality in moderate light conditions (moonlight, areas with low light pollution) |
| 1600+ – 1800+ | Regular use, hiking, hunting, sport shooting | Good balance between sharpness and noise; comfortable for most night shoots. |
| 2000+ | Demanding use, very dark nights | Significantly cleaner image in low-light conditions (new moon, under forest canopy) |
| 2200+ – 2300+ | Professional use, safety, research | Best available performance, sharpest and cleanest image in the worst lighting conditions. |
These thresholds are indicative: the exact FOM varies from tube to tube, within a range linked to the ordered level.
Other criteria not to be confused with the FOM
- White or green phosphor: this does not affect the FOM, but rather the color of the displayed image. White phosphor offers a rendering closer to natural vision and reduces eye strain during long sessions, while green remains the historical military standard.
- Autogating: a technology that protects the tube from bright light sources (headlights, streetlights) and improves contrast in urban or mixed environments. It is a feature independent of FOM, though the two are combined in high-end tubes.
- Generation (Gen 2+, Gen 3): describes the manufacturing technology of the microchannel plate, not the individual performance of the tube. Two tubes of the same generation can have very different FOMs.
How to choose your FOM based on your usage
If you are new to night vision or use it only occasionally, a FOM rating of 1200+ to 1600+ is more than sufficient for getting familiar with the device during hikes or casual observation.
If you engage in the activity regularly and in varied conditions, aim for an FOM of 1600+ to 1800+; this offers the best balance between image quality and budget for hunting, sport shooting, or airsoft.
If you operate in extreme conditions or in a professional capacity, a FOM of 2000+ to 2300+ becomes relevant—particularly for security, search and rescue, or any mission requiring the image to remain usable in the worst lighting conditions.
FOM and choice between LNVM and LAB-NVS
The FOM is chosen independently of the housing. Whether you opt for the LNVM monocular or the LAB-NVS binocular, the same range of NNVT tubes is available—from 1200+ to 2300+—in either white or green phosphor. The choice of FOM therefore depends solely on your intended use and budget, not on the device selected.
Frequently Asked Questions
Does a higher FOM always mean a better image? In low-light conditions, yes—almost invariably. Under a full moon or with supplementary lighting, the difference between a 1400+ and a 2000+ rating becomes less noticeable to the naked eye.
Can the exact FOM be known before purchase? Yes. Each NNVT tube comes with the manufacturer's test sheet indicating the individually measured FOM, resolution, and SNR.
Does the FOM influence the price of the tube? Directly, yes: the higher the FOM, the rarer the tube is during manufacturing quality sorting, which is reflected in its price.
In summary
The FOM remains the best objective indicator for comparing two night-vision tubes, as it combines resolution and signal-to-noise ratio into a single measured value. Rather than basing your choice solely on the tube generation, base your decision on the FOM suited to your actual use: 1200+ for casual use, 1600–1800+ for regular use, and 2000+ or higher for demanding or professional applications.