Since its inception, projection has been the dominant technology for displaying large, high-resolution images. Over the years, projectors have evolved to keep pace with advances in computer graphics and video sources, following the trends toward ever higher resolutions and ever larger screens.
Certain applications, however, such as simulation and training, have always demanded higher pixel densities over larger areas than can be provided by any single fixed projector. This is particularly true where training requirements have an objective of “eye-limiting resolution” over a wide field-of-view, including flight simulation. Such applications are best served by multiple projectors configured in an array, using blending and warping software to stitch the images together to form a composite image with a much higher pixel count.
Moving Toward the Light
With higher system resolution attainable through the use of multiple projectors, the challenges that remain primarily concern reliability, flexibility of projector orientation, ease of setup, and maintenance of performance over time. All of these considerations are greatly affected by the nature of the projector’s light source. This is where LED illumination shines brightest.
Digital projectors have typically used high-intensity discharge (HID) lamps, such as xenon, to illuminate one or more micro-displays. LEDs, however, provide a number of distinct operational and performance advantages over HID lamps that solve many of the remaining challenges of projection arrays in simulators. One of the most prominent benefits is high reliability and long life, with many actual device-hours of testing for LEDs establishing a median lifetime well in excess of 80,000 hours. By contrast, the typical lifetimes of HID lamps can be as little as 500 hours for some high-powered xenon lamps. The longer lifetime of LEDs equates to far less downtime of a projector due to lamp failure and replacement, which means far less downtime for the entire array. It also means a lower cost of ownership by avoiding the material and labor costs of regular lamp changes, including the cost of proper disposal of spent lamps.
LEDs can also operate in more extreme cold and heat, making them better suited for outdoor operation, a strong consideration as the military explores mobile training and simulation platforms that can be quickly set up in the field.
Seeing the Difference with LEDs
Another distinct advantage of LEDs over HID lamps in simulation and training is that they do not generate ultraviolet (UV) light. HID lamps generate a significant amount of UV light that must be removed before it enters the optics of the projector, since its presence can prematurely age optical coatings and other materials. As solid-state devices, LEDs are also very rugged. They can withstand extremely high levels of acceleration and shock — hallmark features of many flight trainers. LEDs can be mounted in any orientation, while HID lamps must almost always restrict their primary axis to a horizontal orientation, with very limited tilt of that axis.
LEDs also allow the design of singlechip DLP® projectors suitable for critical applications, without the need of a color wheel, which is a weak point in the overall reliability of a projector. With a traditional HID lamp as the light source, a single-chip DLP system depends on the use of a mechanical color wheel to cycle between the primary colors during every video frame.
This same ability to directly modulate LEDs in real-time, without depending on mechanical shutters or filters, can enable new levels of system performance and reliability — both within a single projector as well as across an array of projectors. Color balance and overall light levels can be monitored and corrected across a multi-projector network in real-time to optimize the overall display system performance for a given training scenario and specific image content.
LEDs’ True Colors
In recent years, with the growing trend in modern warfare toward “24/7 theaters of engagements,” night vision training is becoming an increasingly critical part of a pilot’s overall instruction.
One of LEDs’ most interesting advantages over HID lamps is their capability to easily generate specific and controlled wavelengths of near-infrared (NIR). By combining a narrow-band NIR LED in the projector’s optical path, along with the usual red, green, and blue LEDs, these projectors are able to generate NIR images to realistically stimulate night-vision goggles (NVGs) — without compromising the color rendering of the image in the visible spectrum. This allows for more realistic NVG training. The ability to precisely control the balance of NIR to RGB light also allows the projector’s output spectrum to be tailored for current or new NVG technologies.
Training and simulation companies, including Aero Simulation, Inc. (ASI), have begun to upgrade their simulators with new projection technology systems, such as the Christie Matrix StIM™, a simulation projection system with LED illumination that is also capable of NVG stimulation. Programs where ASI is using the latest generation of this projection system include upgrades to the existing AH-1W Cobra Weapons Systems Trainers (WST), which directly support Marine Air Group (MAG) 39 in Camp Pendleton, Calif., and MAG-29 in New River, NC; and the development of a new HC- 144A Operational Flight Trainer (OFT), which will be delivered to the Coast Guard’s Aviation Training Center (ATC) in Mobile, Alabama.
As the Coast Guard’s new maritime patrol aircraft, the HC-144A Ocean Sentry has the capability to perform aerial delivery of search and rescue equipment, such as rafts, pumps, and flares. Its modern C4ISR suite, modular cabin, fuel consumption rate, and short field takeoff and landing capability make it uniquely suited for U.S. Coast Guard missions.
The HC-144A OFT is especially noteworthy in ASI’s use of FlightSafety’s CrewView glass-composite collimated mirror system and the Christie StIM WQ DLP projectors with IR illumination to create a large glass-mirror-based visual display system on motion. For the AH- 1W WST program, the IR-illuminated projectors meet out-the-window and NVG visual training requirements for AH-1W flight crews.
A Brighter Future for LEDs
The clear benefits of LED illuminated projectors is leading to their rapid adoption in almost every facet of the government, military, and public sector, including control rooms and signage, where 24/7 reliability is critical. Without a doubt, the future indeed looks bright for the increasing use of LEDs in simulation and training.
This article was written by Dave Kanahele, Director of Simulation Solutions at Christie (Cypress, CA). For more information, visit http://info.hotims.com/49743-140.