This is a much-referenced yet little-understood topic in the NVG world. Most people who insist “I only use GEN3 Tubes!” are often hard-pressed to explain the difference when put to the question, so let’s explore.
The first & most important thing to know is that we like GEN2+ tubes because of their inherent COST / BENEFIT RATIO. In other words, they provide more performance per dollar than other options.
The second thing to know is that “GEN2+” is sort of a misleading term, and can lead one to believe that GEN2+ is “old technology” compared to the “new” GEN3 stuff, and that’s simply not the case. GEN2+ is actually NEWER than GEN3, as far as that goes. To add yet another layer of confusion, the difference between the two TODAY is not the same as it was 5 or even 2 years ago. Gen2+ tubes have seen continual improvement in the last 5 years, especially in terms of Autogating performance, Low Light Sensitivity, Luminance Gain, etc. In contrast, the only notable improvement to GEN3 in the past ten years or more has been the “Supergain” from L3Harris.
So where did the term “GEN2+” come from? In essence, the term was formed around a complex of scientific, political, & international trade influences pushing for a completely different TRADE NAME for a product which differed slightly from GEN3 in materials and technical construction. Indeed, “Gen2+” has more to do with the chemicals and assembly inside the tube than any inherent difference in performance apples-to-apples.
One end result of this is a tendency to associate GEN2+ more with “GEN2” than anything else. Combine that with our good old American habit of hating on foreign-made products (except, of course, our clothes, our computers, our mobile devices, appliances, televisions, cars, vacuum cleaners, and just about everything else we use on a daily basis) and we end up with the general idea that any GEN3 tube, or at least just about any GEN3 tube, is going to perform better in the real world than any GEN2+ tube. Like most things we learn about on the internet, this is just plain wrong.
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The truth is, all other things being equal, GEN2+ is MUCH closer to GEN3 than the older GEN2 technology, in just about every way. One way to think about this, and this paints a pretty accurate picture, is to make the following analogy;
4If GEN3 is the iPhone 17, then GEN2+ is the Samsung Galaxy 22+, and GEN2 is something like the Motorola Flip Phone from 2010.
But we’re getting ahead of ourselves. Let’s start at the beginning. What is the technical difference between modern GEN2+ tubes and GEN3?
The actual TERM “GEN2+” came about from a complex array of scientific, corporate and also political pressures inside and outside of NATO, to come up with a trade name which would distinguish AMERICAN tubes from all others. Think stuffy rooms filled with L3Harris lawyers and their Good Friends in the DOD. But there ARE mechanical differences.
So what ARE the mechanical differences? Well, the TLDNR version is that they use different materials to achieve certain trade-offs in how they perform their task. The largest difference is that GEN3 tubes use a MCP (Microchannel Plate) barrier, or ION BARRIER FILM, which protects the MCP from ionized particles (stuff you don’t want), which are created as a byproduct within the tube. GEN2+ tubes do not have a MCP Barrier, but more on that later. The trade-off with this barrier film is that it can also block photons (stuff you DO want) and reduce overall gain and brightness. (NOTE: This is the “FILM” you hear about when GEN3 tube makers like L3Harris and ELBIT say “Thin-Film” or “Unfilmed”).
GEN2+ tubes require NO Ion Barrier Film, because their Photocathode or “PC” (the section just in front of the MCP) is made of an entirely different material, which does not produce significant ion particles, so the barrier is not needed. The trade-off here is that the GEN2+ PC is fractionally less sensitive to incoming light than the GEN3 type, and therefore overall sensitivity & system gain in extremely low ambient light conditions can be slightly less than GEN3, all other things being equal. This doesn’t make either type inferior or superior in this respect; it merely makes them DIFFERENT, and the 2 construction types result in different TRADE-OFFS.
So how is the Photocathode different? IIn GEN2+ tubes, generally a Multialkali (S-25) material is used, and in GEN3, Gallium Arsenide (GaAs) is used. The development of Gallium Arsenide (GaAs) Photocathodes was largely driven by the complex relationship between the US Military and its private defense contractors, like L3Harris. These developments are proprietary, fiercely guarded by domestic and international laws, and most of all, extremely expensive. When the US military-industrial complex developed GEN3, it was absolutely superior to GEN2 in just about every way, but GEN2+ technology was developed in the years after, not by trying to make GEN2 tubes better, but simply by choosing a different, more affordable material for the PC construction, which also allows for a less complex design overall. A DIFFERENT way to achieve virtually the same results, not an “older” or “inferior” one.
While GaAs offers superior performance in extremely low-light conditions by having higher quantum efficiency in the near-infrared spectrum (around 800-900 nm), and can also allow for overall higher average Luminance Gain, modern high-end Gen 2+ (like NNVT and Photonis 4G) use advanced multi-alkali hybrid Photocathodes that are sensitive over a broader range, including deeper blue/UV light and slightly longer near-infrared wavelengths that GaAs Gen 3 cannot detect at all. This is why many people say that the contrast in GEN2+ I2 tubes can be more “vibrant” to the human eye. Again, as with anything mechanical, these are all trade-offs in taking different approaches to different parts of the tube’s function.
So, summed up, using GaAs GEN3 is not inherently an UPGRADE to GEN2+, or “NEWER” technology, but rather a different technology used for legal, political, and especially cost considerations, with different performance trade-offs to those in GEN3. That’s it!
Taking all this in, it’s important to understand the the most modern, super high performance NVT or Photonis GEN2+ tubes are the equal in every way of super high performance GEN3 tubes. GEN3 tubes can achieve much higher gain levels, as well as higher sensitivity to ambient light in certain parts of the spectrum, than ANY GEN2+ tube. GEN3 tubes can also achieve overall higher signal-to-noise ratios (“SNR”) than even the best GEN2+ tubes. But the point here is not to compare the average NVT tube to the absolute highest spec L3H or Elbit tube. It’s about comparing apples to apples; the real-world difference in performance one can expect between each type during normal use, and is that difference worth the 100%, 150% or even 200% higher cost you can expect to pay for GEN3. Only YOU can answer that question, and we want you to have all the FACTS.
We like Gen2+ tubes because they provide generally about 85-90% of the performance of similarly spec-d GEN3 tubes, for about 60% of the cost, or even less. They last just as long, they pick up a wider spectrum of light than GEN3 but sometimes fractionally less of it, and the trade-offs of very high FOM (2200+) GEN3 tubes are simply not worth the extraordinary extra expense for most users. We say MOST users because some mission parameters & use cases (like Day-Optic Clip-on Devices) sincerely benefit from very high-spec GEN3 tubes, and so we do offer them on a limited basis. Further, some people are willing to pay for FOM bragging rights, or simply from the pride in ownership that comes from having the very best, and we want to serve those customers as well. But for the vast majority of users, we believe our GEN2+ tubes will provide amazing performance well beyond anything you’ve ever expected, at a tremendous value. We guarantee it.
GLOSSARY OF TERMS:
- MICROCHANNEL PLATE: A Microchannel Plate (MCP) is a crucial component in image intensifier tubes (the “heart” of night vision devices) and various scientific detectors. It is a thin, disc-shaped slab, typically made of resistive lead glass, that functions as a high-speed, high-gain electron multiplier. Electrons fed to the MCP by the PHOTOCATHODE are multiplied in number exponentially, and passed on to the PHOSPHOR SCREEEN.
- ION-BARRIER or “FILM”: This film is an ultra-thin layer of material, typically sintered aluminum oxide, deposited on the input surface of the microchannel plate (MCP). Its purpose is to
- FOM: Acronym for Figure Of Merit; an “at a glance” spec which can give an overall idea of the tube’s level of performance
- PHOTOCATHODE: The Intensifier Tube component that is responsible for converting incoming photons (light particles) into electrons through the photoelectric effect. These electrons then pass to the MCP
- PHOSPHOR SCREEN: The phosphor screen in an intensifier tube is a complicated micro-sandwich of phosphorescent chemicals and substrates, which becomes electrostatically excited when hit with electrons exiting the MCP. The screen converts a wide spectrum of light into the visible spectrum, and passes that image to the output lens
- LENSES or “Glass”: The optical lenses used to collect and pass on ambient light on the objective side, and send a coherent image to the user’s eye(s) on the Ocular side.
- SIGNAL TO NOISE RATIO or “SNR”: A fundamental metric that quantifies the strength of a desired signal relative to the level of unwanted background noise present in the same system. Here, it is the amount of ambient light collected across the entire spectrum that is effectively passed to the user, versus “noise” and artifacts created by the process.
- RESOLUTION or “RES”: A measure of the tube’s ability to distinguish fine details in the very middle of the image. It is a key specification that indicates the sharpness and clarity of the core image, measured in line pairs per millimeter. Center resolution is measured in a controlled laboratory setting using a specialized night vision test set and a resolution test chart.
