After a cursory analysis, it may seem that all display technology is basically the same and a standard liquid crystal display (LCD) commercial product will be adequate for your program. A closer examination of advanced LCD functionality reveals multiple ways an application-specific display will improve operating safety, enhance end-user efficiency, and reduce complete lifecycle costs.
This paper first discusses advanced capabilities that enhance LCD technology and then reviews business factors to consider when selecting or specifying display systems.
Effective Night Vision Imaging Systems (NVIS)
Most aircraft and land system displays need the ability to provide clear, easily viewed images during both day and night operation. These displays are all equipped with a day/night switch, but there is great variation in the quality of NVIS support and what the end user really sees. Two common issues are night vision ‘blooming’ and uneven image luminance during night operation.
‘Blooming’ is a huge problem for end users with night vision goggles. A standard laptop experiences blooming when the brightness setting is taken to its lowest viewable setting, or steps down luminance for its light emitting diodes (LEDs) to a lesser percentage when switched to night mode. The same effect occurs in some deployed helicopters and ground vehicles, impacting warfighters’ situational awareness and reaction efficiency. A commercial-grade NVIS filter can be used, but this often effects the red chromaticity, giving images an orange hue. This, in turn, reduces the light transmitted through the LCD, making details less clear across all sections of the image.
Blooming can be eliminated if the display implements a true dual mode, with separate day and night backlighting approaches. This type of dual mode backlighting may offer either white or RGB LEDs for daylight operation and separate NVIS-compatible LEDs for night operation. The NVIS backlighting LEDs should be capable of a wide range of luminance from 650–930nm. Very low-level luminance can be achieved by a burst modulation scheme; an explicit NVIS LED wavelength cutoff below 650nm goes even further to prevent NVIS blooming.
The second night operation issue, uneven display luminance, is also common in commercial, and even industrial, quality displays. When night mode means reduced luminance, light is no longer distributed evenly across the display and ‘spotlights’ appear on the edges, interfering with end-user image perception. The same separate NVIS LEDs used to eliminate blooming also can be equipped with optimized, display specific light guides that spread the low-level light evenly across the display so there are no spotlights.
The flip side of effective NVIS is effective sunlight readability. In the bright light of a desert, tropical ocean, or arctic environment, the challenge is to deliver more luminance to a display so that image details can still be easily seen by end users.
Commercial-grade LCD displays use lower-cost COTS LEDs and operate them at close to, or above, 100 percent of their maximum voltage during normal operations, so there is no headroom for a luminance increase in bright sunlight. One path to a solution is to use LEDs that normally function at less than half of their rated power capacity, so there is room to incrementally increase luminance over time, as the LED inevitably will degrade. This desired longevity effect can be further enhanced if an etched light guide is used to diffuse the light from the LED, maximizing its effectiveness.
These solutions are also useful in dealing with a related issue, extended display life, which is discussed later in this paper.
Displaying All the Image Details Available from a Sensor
The bit depth of a display is key to delivering image details
Modern display systems must be able to present sensor information to end users with as much detail as possible. Using a display without enough bit depth to closely match the sensor video output means that critical details will be lost. At the same range, an image only distinguishable as a human being at eight bits can be clearly identified as an armed warrior wearing typical NATO standard dress and carrying a typical NATO M5 weapon at a higher 10-bit gray scale, matching the 10-bit sensor.
Effective display of today’s sensor technology is achieved with a 10-bit native display (30-bit RBG), creating images with 1.3 billion colors and 1024 shades of gray. This grayscale depth, even using XGA standard resolution and 1:1 pixel matching to a thermal imaging (TI) sensor, renders an image perceived by end users as HD quality. Current applications of thermal imaging offer an increasing ability to discriminate at long range, but are only maximized when paired with a 10-bit display that closely matches the thermal imaging raw video output capability.
Ten-bit displays are also highly effective for all types of night vision imagery, especially when compared to 8-bit displays. The two extra bits of grayscale depth give users a fourfold increase in image clarity (from 256 > 1024), allowing them to identify details in images with limited dynamic range. The extra bit depth adds both subtlety to the gradations in tone that are displayed and the range to obtain the higher clarity. For color images, the added bit depth allows smoother color transitions that significantly improve user accuracy in interpreting fine details. This is especially true when the images are from a modern 12-bit or higher color camera. Ten-bit capability makes images look natural and smooth, delivering undetectable color transitions.
How an LCD Works
An LCD consists of a liquid crystal fluid in between two pieces of polarized glass, aka substrate. A backlight, typically from strings of LEDs, creates light that passes through the first substrate. Low-voltage electric currents from the display controller cause the liquid crystal molecules to align in ways that allow various levels of light to pass through to the second substrate, creating colors and images.
To further enhance user perception of imagery, displays can use specifically manufactured LEDs that are color matched with the phosphor content of the LCD color filters. By controlling the color filter selection of the LCD and the phosphor selection of the backlight LEDs, a display’s optical performance is maximized.
Using increased color depth and LED color matching delivers impressive increases in end-user image perception with a huge systems engineering advantage; the platform network does not have to be redesigned to achieve a better image. Some platform upgrade requirements now specify HD imaging systems when, in fact, the display components are incapable of rendering HD images without a wholesale replacement of the supporting vetronics infrastructure so it can support HD bandwidth requirements. A better solution is to simply use displays that fit the current network but are enhanced to get the most out of the sensor imagery and then modify the sensor video processing algorithm to output in higher-color depth and grayscale.
Optimized Images for Multiple Applications in One Display
Because humans have better perception of differences between darker tones than lighter ones, most applications use a gamma encoding of imaging to optimize the use of image signal bits. Without gamma encoding, applications would allocate too many bits (and too much bandwidth) to highlight differences that humans can’t differentiate and too few bits to shadow values where humans are sensitive, reducing visual quality.
However, optimal gamma encoding varies by the display application. It is commonly around 2.2 but may be .78 for a thermal-imaging application and 1.8 for a battle graphic. On today’s platforms, most displays are supporting between three and six different applications. To deliver the best possible visual quality to the end user, these displays need to have simultaneous support for multiple gamma encoding values, with seamless matching of those values to the appropriate application controlled windows. No commercial-quality LCD can deliver that capability without customization.
Eliminating Windscreen or Bubble Canopy Display Reflections
Aircraft crewmembers have long struggled with reflections on the windscreen or bubble canopy from flat panel cockpit instrument displays. The wide viewing angle of a normal LCD, very desirable when watching TV at home, floods a cockpit with light, often with some images reflecting off the windscreen or canopy glass. This problem is especially acute during night visual flight rules (VFR) operations. The reflected images may distract pilots, interfere with their long-range vision through the canopy, and even cause disorientation. The overall effect can be distracting or, worse, life threatening.
Now it is possible to eliminate undesirable canopy reflective optics by controlling off-angle luminance with a tightly packed array of fiber optic elements embedded in the display glass. Each fiber is coated in a black cladding and is many times smaller than the pixel window of an LCD. These innovations deliver an effect similar to looking through a matrix of packed straws; the view is clear directly in line with the straws, but blocked if viewed from the side. Light from a display is directed into a desired viewing angle, making it easily visible only for the pilot or copilot, without the stray light optics that cause cockpit reflections.
Bubble Canopy WP: https://www.mrcy.com/resourcehub/avionics/dualredundant-display-in-bubble-canopy-applications
No Single Point of Failure
Aircraft designs have advanced steadily in providing pilots and aircrews with fully integrated flight information. A key component for the realtime information access is a large area display (LAD) that presents clear, crisp, high-fidelity images across multiple windows and video overlays. These displays, 20-plus inches diagonally, are also equipped with touch technology similar to smartphones and tablets.
With flexible windows and touch controls, a single LAD replaces multiple system-specific displays and controllers. Navigation, weapons control, engine control, communications, tactical situation monitoring and other systems are all viewed and controlled using the LAD, reducing the overall weight and power requirements. Equally important, users have the flexibility to enlarge or reduce the display area devoted to any system, based on immediate mission need.
While a large cockpit screen delivers great application flexibility, a single monolithic display also represents a single point of failure. If it stops working, all the systems ‘go dark,’ putting the aircrew in a lifethreatening situation.
An elegant and effective design solution is achieved by implementing two independent cells on a single LCD substrate, with no visible vertical gap down the center of the display. While they can display a single image with no visual separation, there is redundancy between the two cells. Multiple windows can be displayed, driven by multiple applications, and moved seamlessly between the two halves of the LAD. However, if one cell fails, the other still provides display support for all the aircraft systems.
Operating in Extreme Temperatures
If a commercial-quality LCD screen is operated in a warm-weather environment and then exposed to direct sunlight, the temperature can quickly reach a point where the liquid crystal material no longer functions. Higher-quality display fluid is needed for high-temperature operation. On the other hand, in temperatures below -20°C, the liquid crystal material begins to thicken, reducing its reaction to small voltages and thus changing what is displayed on the screen. The solution for this is the addition of a heater element to the LCD, which permits normal operating performance at cold temperatures and reduces the amount of warm-up time required from a cold start. Depending on the expected range of operating environments, displays for aircraft and defense platforms may need designs that can deal with both types of extreme temperature.
Closely related to some of the technical issues already discussed, there are a set of often-overlooked business factors to consider during evaluation of deployable displays. These factors directly impact the total cost of ownership for a program and should not be underestimated.
Extended Display Life
Replacing an aircraft or ground vehicle display panel is expensive and can interfere with mission availability. Extended display life mitigates these issues, with economic and operational improvements proportional to the life extension. Display life is usually quantified utilizing mean time between failures (MTBF), a convenient measure of reliability.
Higher-reliability designs begin with flexible control of luminance. As referenced above, commercial-grade LCDs must often be driven at 100%, or higher, of their rated voltage potential just to yield sufficient luminance for an effective user interface, especially when operating in direct sun/daylight conditions. This reduces display longevity, as LEDs continuously delivering maximum capacity luminance degrade quickly. On the other hand, display MTBF is increased significantly by using LEDs that can normally operate at some fraction of their maximum capacity, only increasing luminance when needed.
LEDs with extra luminance capacity can further increase MTBF when combined with an adaptive design. Over time, some strings of LEDs, in any display, will inevitably fail. An adaptive LCD implements high-density LED packing, then uses internal luminance sensors to detect when a string of or single LED has failed. At that point, the luminescence of adjacent strings are increased to compensate; the user will not perceive any difference.
Working in combination, these design features result in displays with reliability that far exceeds anything offered by standard commercial or industrial products. The value of the difference in reliability should be included in any life-cycle cost analysis.
Embedded Systems Business Practices
In addition to the unique technologies that support deployable displays, programs for aircraft and ground vehicles need partners who support embedded systems business practices.
A commercial LCD provider cannot make any guarantee for performance in a deployed systems operational environment. In fact, a commercial warranty is voided when the LCD materials are operated outside of normal office conditions. Deployed systems need display designs that can be customized to meet requirements for both environmental conditions and optics.
Equally important is a long-term commitment to availability. A commercial display product typically offers one year of availability; replacements after that year are not one-to-one and often require platform design modifications. Programs need some guarantee of product continuity to avoid disruptive, expensive, and time-consuming redesigns.
Display Innovations from Mercury Systems
For more than two decades, Mercury Systems has worked to improve deployable displays, developing unique, patented technologies. Innovations include:
• True dual-mode (day and NVIS) backlighting, both equipped with optimized light guides.
• Customized LEDs that can operate efficiently at 30 percent of their maximum voltage capacity.
• A choice of 8-bit or 10-bit color depth LCDs.
• Displays supporting 16 different values for gamma decoding, which can be applied individually to 16 separate inputs.
• Fiber-optic elements embedded in the display glass, eliminating bubble canopy reflections.
• Redundant LAD technology, offering independent power and video paths for each of two displays, residing on a single LCD substrate.
• LADs with no visible vertical gap down the center of the display, as the separation between the cells occurs at the sub-pixel level, not discernable by the unaided human eye.
• LADs supporting both flight- and arctic-gloved hand touchscreen operation.
• Displays that use customized liquid crystal material to operate at high temperatures and a thin coating of indium tin oxide that functions as an embedded heating element for cold temperatures.
• LED packing at roughly twice the density of commercial LCDs, combined with internal luminance sensors, to detect LED string failures and increase luminance on adjacent strings.
• A set of technologies and design techniques that support a MTBF nearly seven times longer than standard industrial grade LCDs.
Mercury’s technology innovations are matched by a 10-year form, fit, and function display availability, eliminating redesign issues.
A Track Record of Success
Mercury Systems is an industry leader in high-performance displays for military aircraft and ground vehicles. Their displays are found in the world’s premiere fighter aircraft cockpits, such as the F-22, F-35, and EF-1000 Eurofighter. They are in rotary aircraft, such as the AH-64 Apache, UH-60, CH-46 and CH-47. Within land system vetronics, they support General Dynamics Land Systems’ M1A2 and M1A7 (SEPV4) Abrams Main Battle Tank and M1128 Stryker Mobile Gun System ground vehicles. These high-profile programs represent just a few of Mercury’s deployments.
Mercury’s contributions to commercial aviation are no less significant, providing a continual range of square-glass products, dating back to the first glass cockpits displays. The Boeing 717-787 and Airbus A-319 / 320, 330 and 340 aircraft are all currently operating with Mercury displays.
Engage with Mercury, A Trusted Display Partner
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Sr Manager, Sales / Business Development
Mercury Mission Displays