Unrivaled Unfilmed Gen III Image Intensification Tube Technology

Three generations of image intensifier tubes have been formally assigned by the US Government: Gen I to Gen III. The generations correspond to major tube construction changes that provided significant capability advancements. For example, Gen II added a microchannel plate (MCP), increasing gain dramatically, while Gen III introduced a gallium arsenide (GaAs) semiconductor photocathode design for better sensitivity, especially in the near-infrared range.

Reference the Military-specified generations chart above.

View the Gen III Image Intensifier Tubes Guide to Tube Technology

The primary difference between Gen II and Gen III tubes is the photocathode material. Gen III uses crystalline gallium arsenide, often given as its chemical name GaAs, which offers a higher sensitivity in the near infrared wavelengths available in dark night skies, resulting in higher real-world performance as measured with higher gain and signal-to-noise ratio (SNR).

There is no formal definition for ‘Generation IV’ by the US Government. The term was briefly considered for unfilmed or filmless tubes due to their higher performance. Some marketers use '4G' to imply a 4th generation tube, but it remains a Gen II device.

Reference the Military-specified generations chart above.

View the Gen III Image Intensifier Tubes Guide to Tube Technology

Yes, an image intensifier tube can operate for a time in a lit room or during the day, but its performance will be degraded to protect it from immediate damage. However, even with this self-protection capability, the tube may be damaged or lose gain performance within minutes or even less if the scene brightness is excessively high. A lit room is typically 10-100 times dimmer than an outdoor scene during the daytime, generally making the tube more forgiving in these scenarios. To minimize degradation, you should stow or turn off the goggles when the brightness levels are high enough for normal vision without night vision aids.

"Figure of Merit" (FOM) is a metric used to represent the general performance level of an image intensifier tube. It was developed to provide a simple way to gauge the range performance of a tube. Although not a precise correlation to detection, recognition, and identification (DRI) range, FOM offers a way to compare overall tube performance under standard conditions. A higher FOM, such as 2500 compared to 1600, does provide much higher resolution and sensitivity in low light environments, which is readily seen and valued by experienced customers who need the best performance possible in life safety situations.  

Reference the Military-specified generations chart above.

Sky glow is the background light from the night sky that is separate from man-made light sources such as urban light pollution, and the contribution of stars, planets, and the moon. It is mainly scattered light due to radiation generated by molecules in the atmosphere. Both moonlight and skyglow provide illumination for night vision devices in dark areas and contain more near-infrared light than visible light. This is partly why Gen III tubes are so widely adopted and capable of operating at higher gains to support operations in darker conditions.

Halo is an effect where bright lights within the night vision scene create a diffuse area of added brightness surrounding them. It is caused by primary electrons interacting at the microchannel plate (MCP) input surface, producing secondary scattered electrons that spread out. This is most visible in areas of high contrast, like around vehicle headlights or building lights. 

L3Harris’ unfilmed tubes can offer the smallest halo by using an anti-scatter layer on the MCP input surface. This technology reduces the halo effect, sharpening the entire image and improving visibility near bright-light sources.

Resolution is measured using the USAF 1951 tri-bar pattern assessment method, requiring a 10X magnifying optic to determine the tube’s limiting resolution. Values like 64, 72, and 81 line pairs or cycles per millimeter are reported based on the smallest resolvable pattern by the tester. Factors like eye fatigue and tester experience impact these results. The US Army specifications do not permit interpretation or averaging of results beyond standard values.

Others that provide data with in between values are not using USAF testing methods.

Tubes only lose gain through use at varying rates based on the manufacturer, related to overall light exposure and electron release during operation. When stored in cool, dark conditions, tubes are expected to retain gain life until the vacuum seal degrades. Most tubes will remain unaffected for 10-20 years, with many expected to survive for well over 100 years.

Tubes can be damaged very rapidly if exposed to extremely high light intensities, such as direct sunlight or high-intensity lasers. In bright environments like a lit room, damage takes much longer but can happen. Recovery from excessive duration high light exposure is possible with long exposures to a uniformly lit wall but is not guaranteed. The standard test for high light durability exposes a tube to a bright source, comparable to a car headlight at a short distance away for 60 seconds, ensuring no noticeable image burn-in after a recovery time.

Temporary dark streaks are caused by film charging effects in legacy filmed tubes, where electrons from the photocathode accumulate on the MCP surface film. This reduces brightness and is more pronounced in older films. Newer unfilmed tubes greatly reduce this effect and significantly reduce the time to fade out. 

The tube’s auto-gated power supply instantly controls tube currents to ensure normal operation and limit damage, making the scene appear normal in a fraction of a second. During ultra-high light exposures, the tube may dim momentarily, and the recovery time from extremely bright flashes may take a noticeable fraction of a second. 

All modern image intensifier tubes use automatic brightness control (ABC) that actively adjusts the tube gain as the display output brightness level increases above a preset threshold of approximately 10 nits. The ABC circuit serves to provide a stable output brightness for the end user in widely varying brightness conditions ranging over a million to one range (from approximately 0.001 to over 1000 lux at the tube input, roughly corresponding to moonlit and brighter scenes). This ABC feature is very fast and will react in a fraction of a second such that a huge brightness change will only appear as a momentary flash before recovering to normal display brightness levels. Additionally, most systems include external gain adjustment control (EGAC) that allows the user to manually override the factory-set maximum tube gain setting on the tubes, as desired, in order to better suit their needs.

These frames are 1/30 second apart. Recovery back to frame 1 is instantaneous.

L3Harris tubes are tested to meet stringent US Army requirements, including temperature ranges from -54°C to +85°C for storage and as low as -51°C to +52°C for operation. Rigorous environmental testing ensures ongoing compliance with military standards. These temperatures apply to the tube only and the system specifications may vary. 

L3Harris has a world class quality management system to ensure robust and rugged environmental reliability.

L3Harris’ unfilmed tubes can withstand significant shock loads, demonstrated with up to 0.50-caliber rifles, without damage due to the absence of an ion-barrier film. This makes them highly resistant to shock-induced damage or performance degradation.

Equivalent Background Input (EBI) refers to the tube's output brightness with no light on its photocathode. High EBI values can reduce the imaging contrast range, particularly in higher ambient temperatures, affecting detection, recognition, and identification (DRI) performance. Unfilmed tubes from L3Harris offer the best EBI available.

External Gain Adjustment Control (EGAC) allows users to override the tube’s standard gain to manually manage screen brightness, which can be desirable in certain situations. A broken EGAC connection will be detected and while it will disable the gain control feature until repaired, it maintains normal operation rather than be stuck in a low gain state. This ensures the tube remains usable until repaired so the user is always able to perform their mission. L3Harris tubes can have the EGAC flex tail replaced without damage, although system disassembly is required.

High light resolution measures the tube's limiting center resolution at the equivalent to dusk conditions where night vision is rarely, if ever, used or needed. L3Harris prioritizes optimization for ultra-dark conditions while balancing high light capability with tube durability.

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The hexagonal grid arises from the manufacturing process of the microchannel plate (MCP). The hex pattern is more noticeable at very low gain levels and is due to slight distortions at the hex fiber boundaries within the MCP. This effect can be most noticeable in higher light scene levels, especially with higher performance tubes that have high gains

These are small defects that appear as dark or bright points in the field of view, resulting from tiny imperfections in components or particles during manufacture. Inspecting each tube for compliance, L3Harris minimizes these imperfections, though some may still occur.

This sound results from autogating operations, where time-varying voltage creates forces on the components, making them resonate like a tiny speaker diaphragm. L3Harris suppresses this effect using its electronic design to ensure audible security for its users.  

This image shows distortion of an MCP under the force of the applied voltage.

They both can use the same tube inside and do not affect the imaging performance, they only impact the electro-magnetic interference (EMI) performance in a system. We default to metal housings for the best available performance offerings to our customers.

White phosphor provides a more natural view, with better contrast and detail resolution. It enhances performance in ultra low-light conditions where the human eye is more sensitive to blue light and our tubes present imagery in a broad light spectrum, enabling users to see a wider range of visual details.

You can see blue light much better than green when it is really dark, which is why we have blue phosphor. Dark-adapted eyes use rods more than cones.