Seeing the Light
Achieving Full-Color, Day or Night Readability for Flat-Panel Displays
In order to meet the requirements of current-generation military ruggedized displays and monitors, various technology innovations have been developed that allow for an enhanced user experience. Accommodating all of these needs has become a challenge for design engineers, especially when it comes to aircraft displays and monitors.
The avionics systems used in military aircraft incorporate flat-panel displays that must be readable in all levels of light. However, many traditional displays do not provide color uniformity in ambient lighting with night-vision goggles (NVG) compatibility unless night-vision imaging system (NVIS) filters are applied. Despite the need for flat-panel displays to support seamless sunlight to nightvision transitions with full-color, these NVIS filters continue to be used in military and aerospace applications.
To meet this challenge, the design engineers at Daisy Data Displays, Inc., a ruggedized military computer and display manufacturer, have developed a NVIS technology for military and flight simulation displays and monitors that provides full-color readability in daylight and with NVIS goggles without the need for add-on filters. The technology eliminates expensive additions or processes traditionally used to support the transition.
Eliminating LCD Backlight Filters
Night-vision imaging systems require more than just goggles. Most of the lighting inside of a night cockpit contains infrared light that causes goggles to “bloom” or “halo”. This means the images seen through the goggles are degraded and are so bright that key visuals become obscured. Eliminating this issue for flat-panel displays has historically been achieved by implementing a poly-based filter in front of a liquid crystal display (LCD) backlight via snap-on clips or adhesives. These filters can also be integrated into the backlight.
These traditional NVIS filters are not only expensive, but they typically yield a green or low-color on-screen data view to the entire LCD, restricting the readability of the display. Important readouts, such as red warning lights, are difficult to see with NVIS goggles. The red colors appear as an orange tint known as NVIS Red. Combined with the long lead times and quality concerns associated with NVIS filters, these visual and color interface issues were a major catalyst in the development of an alternative technology for NVIS applications that would allow for color uniformity without filters.
In 2006, sunlight and NVIS switchable products were introduced, with a 10.4” touch screen x-terminal, known as the Model 7171CA. The Model 7171CA used a transflective LCD with a modified cold cathode fluorescent lamp (CCFL) backlight rail system that was capable of NVIS-only backlighting and high standard backlighting with the push of a button.
Since then, there have been significant advances in the capabilities of sunlight readable and NVIS technologies, such as light emitting diodes (LEDs). As LEDs began to replace cold cathode fluorescent lamps (CCFLs) as the primary backlighting for LCDs, Daisy partnered with several LCD backlight suppliers to explore possible solutions. However, it was not until recently that they developed a design solution that would meet all of the requirements and feedback specified by potential military and flight simulation users.
Incorporating Hot Mirror Technology
This NVIS technology solution integrates a specialized dielectric mirror known as a “hot mirror” that is specifically tuned for the backlight of the LCD display that is being used. Hot mirrors are used to protect an optical system by reflecting infrared light back into the source and allowing visible light to pass. This eliminates only the wavelengths that will affect NVIS goggles and allows all other wavelengths to pass through. This leaves the colors of the LCD appearing more vibrant and clear on screen, unlike the green tint emitted by conventional NVIS filters. This is what allows the full-color display interface to exist in both indoor, ambient light conditions and with night-vision goggles.
The hot mirror is an appropriate solution for the military and aerospace applications, which have the highest demand for NVIS capabilities. In order to comply with Class B Night-Vision standards and MIL-STD-3009, the design engineers tuned the hot mirrors specifically to cut the wavelengths of light off at 665 nm. This is specified by Class B Night-Vision standards, a classification of MIL-STD-3009 that indicates that a display’s lighting components are compatible with night-vision goggles with a 665 nm minus-blue objective filter.
MIL-STD-3009 is a significant standard for the technology to meet because it establishes the requirements for the emission of all aircraft lighting and display equipment used with NVIS. By designing a display that is compliant with MIL-STD-3009, users have the ability to rapidly and accurately obtain crew station information without any adverse effects while using NVIS.
Achieving Enhanced Usability
The majority of night-vision displays are used in applications where NVIS goggle compatibility is only required 20% of the time, and traditional filters cause the green or low-color tint 100% of the time. This means that displays equipped with the NVIS technology must be readable under normal, indoor lighting conditions. This makes the low-color screen tint an undesirable feature. A major objective of this technology is to provide an interface that appears like a typical office LCD at all times and does not cause eye strain, fatigue, or distractions to the user.
To meet these specifications and improve ease of use, user feedback was integrated into the design of the technology. Potential users were provided with several NVIS switchable solutions in which the NVIS brightness was always lower than what was required—first in the 0-2 NIT range, then in the 0-5 NIT range. The screens achieved acceptable readability in daylight, but lacked the level of brightness required for NVIS goggle compatibility. By eliminating the switchable backlight system, the design is simplified, and the brightness range increases to the 0-35 NIT range. This provides the full-color, normalized interface that most users desire.
Newer models equipped with NVIS capabilities have the ability to switch from day- to night-vision by pushing a button. This immediate transition is unmatched by traditional poly-based filters that are used to support NVIS goggle compatibility. To achieve this full-color NVIS solution, the brightness range of the backlight must be modified. In dual backlight monitors, a non-NVIS backlight is switched on or off when the button is pushed.
This NVIS technology solution can be applied to various sizes of LCD display with LED backlighting systems. However, the largest LCD displays that the technology has been applied to are 24" with screen resolutions of up to 1920x1080. Although it could be specified for LCD displays in any application, the technology is designed exclusively with military and flight simulation applications in mind.
The United States Coast Guard utilizes this technology to meet NVIS requirements aboard select Lockheed C-130H military aircraft. As the chief support aircraft for the US Coast Guard, the C-130H is active in various operations, such as long-range search and rescues, homeland security patrols, and logistics that require displays with the ability to support uninterrupted day to night transitions. The C-130H’s two-pilot flight station is complete with digital avionics, heads-up displays, and a state-of-the art navigation system. This fully-digital interface must be readable in all levels of light, and the NVIS technology was a reliable solution. Equipped with this technology, flat panel displays can provide unmatched advantages to users in military and aerospace applications.
This article was written by Michael Hadaway, General Manager, Daisy Data Displays (York Haven, PA). For more information, Click Here .