Screens in the Sun
Written by Cheryl Gerber
One of the chief considerations when deciding which rugged laptop to use is the display technology. A screen that is shiny indoors, with sharply defined images and rich colors achieved by forfeiting the antiglare coating, can become a blinding mirror outdoors in the bright sun, rendering the screen unreadable.
Technology improvements in the past decade have made rugged notebook displays increasingly easier to read in the sunlight. Until this year, however, it was still difficult to see the detailed color variations on a touch-screen, for reading maps under intense direct sunlight, for instance, without prematurely draining the battery.
The size and design of a screen, its impact on battery life and performance, its weight and cost all must be taken into consideration. There are also circumstances when the use of a touch-screen is required. It’s a balancing act of tradeoffs that the Army Program Executive Office Command, Control, Communications Tactical (PEO C3T) at Fort Monmouth, N.J., has been tackling for more than a decade, and has only grown more pressing as U.S. forces operate in the harsh terrain of Southwest Asia.
“The definition of requirements is really important in the selection of rugged notebook display technology. Out in the desert where the sun is bright, you want to make sure your screen is easily readable without causing too much stress on the human eyes so the users don’t get fatigued,” said Ashok Jain, product director for common hardware systems under Army Project Manager, Tactical Radio Communications Systems (TRCS).
By its very nature, a battlefield requirement demands the most from technology. “The users want it rugged, with large screens and more battery life, but less weight. And they need it to be highly reliable under varying conditions in extreme hot and cold temperatures,” said Jain.
There are certain assumptions for rugged notebooks with outdoor screens. For example, all of them have anti-reflective coatings, since the designation of rugged implies outdoor use. And anti-glare coatings aren’t the same as anti-reflective. They don’t merely reduce the light reflected by the screen.
“Anti-glare coatings scatter or diffuse the light, so all you can see is an indistinct blob, rather than a clear image,” said Geoff Walker, principal, Walker Mobile, an independent mobile computing consultancy.
Fort Monmouth uses Panasonic’s Toughbook CF-30, the latest, full-sized, rugged clamshell notebook with a touch-screen, its predecessor, the CF-29, as well as the CF-19, the latest rugged Tablet PC with a touch-screen.
“Every Toughbook we make has at least an anti-glare coating, whether it’s for business or military, because even fluorescent lights in an office can make it difficult to look at a display if you don’t have an anti-glare coating,” said Kyp Walls, the company’s director of product management. “For the screens intended for use out in the sun, we added an anti-reflective coating to the anti-glare coating, but anti-reflective coatings are more complex and expensive.”
When Panasonic introduced its first Toughbooks 11 years ago, they had both anti-glare and anti-reflective coatings with a 180 nit brightness rating, but customers still had difficulty seeing the images clearly when they were outside under the sun, and the displays drained the battery life.
“We started improving individual components to increase the brightness of the display incrementally, from 250 nit, then to 500 nit in the Toughbook CF-29, but in harsh direct sunlight, it was sometimes still difficult to see the screen, so we increased it again in the Toughbook CF-30 touch-screen, added an extra bulb and brought it up to 1,000 nit,” Walls said. “We managed to achieve the 1,000 nit display with only a 10 percent decline in the battery life, which still has a 4.65 hour life.”
TOUCH-SCREEN ISSUES
The brightness of a display is measured by the number of candelas per square meter, or nit, based on the Latin word “nitor,” meaning luminosity. There are two chief methods of designing a screen to be readable outdoors. One is to increase the brightness (measured in nit) of the backlight to a point where the light emitted by the screen is more than the light reflected by screen. The other is to treat the surface of the screen to reflect less light.
Today, the standard screen is a backlit thin film transistor (TFT), liquid crystal display (LCD) with cold cathode fluorescent lamp (CCFL) backlighting and varying layers and types of treatment to reduce reflections from the surface to varying degrees.
Traditionally, it has been more difficult to produce touchscreen displays that are readable in the bright sunlight, since the multiple layers of a touch-screen create so much reflection. And the tradeoff is this: Cranking up the nit to 1,000 lowers the battery life.
“The number-one power consumer on laptops has always been the LCD display. But we also provide user control with a function key that has 20 options for brightness or dimness,” said Walls. “The Panasonic Toughbook CF-30 and the tablet, CF-19, are fully rugged and meet all military specifications.”
There are three main types of LCD’s, each with pros and cons: transmissive, reflective and transflective. Transmissive LCD’s use a backlight and have been widely used in notebooks indoors, but can only be used in the shade outdoors, as direct sunlight overwhelms the backlight. Reflective LCD’s use available ambient light, which passes through LCD layers to a mirror, reflecting it back to the viewer. They are inexpensive but require bright light, therefore limiting low light or night viewing. However, adding frontlights can improve the viewing in low-light environments.
Transflective LCD’s use both transmissive and reflective methods, by incorporating a backlight and a reflective mirror that lets light pass through in order to give users better viewing under both dark and light conditions. The method cannot do both well, as they are not dedicated, so they are not as bright indoors as a transmissive LCD or as bright outdoors as a reflective LCD.
The size of the screen also creates variations in the weight and battery life of the laptop. Larger screens weigh more and drain the battery more. It also depends on how much larger the screen is. “You don’t have to draw more power from the battery for backlight on a display unless it’s significantly larger, like from a 12-inch to a 15-inch display,” Walls pointed pointed out.
The Panasonic CF-19 rugged Tablet PC has a 470 nit touchscreen that is 10.4 inches and weighs only five pounds, compared with the more robust CF-30 with the 1,000 nit touch-screen, which weighs 8.4 pounds with a 13.3-inch touch-screen. The Army PEO at Fort Monmouth has also begun to use General Dynamics Itronix ultra-rugged XR-1 as well as the semi-rugged Itronix VR-2, both with DynaVue technology that make the touch-screen readable in bright light.
When General Dynamics Itronix introduced Dynavue in June, it released a touch-screen breakthrough at the highest level of outdoor readability, according to Walker. “Itronix really did do something that nobody else has done,” he said. “They integrated the LCD and the touch panel by moving the polarizer that is on top of all LCD’s to the top of the touch panel.”
RESISTIVE DESIGN
In resistive touch-screen design, stacked layers of different materials sit atop the LCD. To create DynaVue, Itronix engineers moved one of the layers—a polarizing film that was situated lower in the LCD stack—up to a position just under the surface of the actual touch-screen, thereby eliminating light reflected off all the layers inside the touch-screen.
“By moving the polarizer up, changing it from linear to circular polarization and using a high-quality anti-reflective coating on the top surface, Itronix got the reflection down to slightly less than 1 percent without any significant loss in display brightness. It’s amazing performance for a resistive touch-screen,” Walker said.
“We used polarizing films, like what you see on polarizing sunglasses, and index-matching films at the front of the touchscreen stack to reduce reflection. We achieved three main benefits. First, we have a better contrast ratio so you can see the fine details of colors. Second, we de-coupled the display from the battery life, so we are not using additional battery life to power up the display. And third, we de-coupled the display from the processing architecture, so we can use a full voltage processor if we want,” said Ben Thacker, vice president of strategic marketing, General Dynamics Itronix.
Indexed-matched coatings help to transform the frequency of the reflected light waves to eliminate the reflections that make displays unreadable in sunlight. The contrast ratio is the difference between the whitest white and the blackest black, according to Walker. “Outdoor readability is really all about contrast, not brightness.”
GD Itronix says its DynaVue technology strikes a balance between display brightness and contrast ratio. The company uses a single cold cathode fluorescent lamp (CCFL) to provide brightness without susceptibility to heat damage from using extras CCFLs and without sacrificing battery performance. The lighter display keeps the overall unit weight down, and the technology meets MIL-HDBK-87213, a military standard for electronically generated airborne displays for the ability to view in direct sunlight. Earlier this year, Walker conducted a comparative review of notebooks with outdoor-readable screens for RuggedPCReview.com.
For a display without a touch-screen, he chose the Dell ATG 630 semi-rugged notebook. “The Dell is definitely my top choice for a sunlight-readable notebook in this category,” he said.
The Dell screen has a brightness of 500 nit, which, according to Walker, is 2.5 times that of a standard notebook. The system also boasts a high contrast ratio, owing to a Dell design that uses an optically bonded anti-reflective, coated cover glass to the LCD.
STANDARDS TESTING
Augmentix renders a Dell Latitude ATG (All Terrain Grade) more rugged by redesigning the chassis and the thermal systems, then testing the resulting ruggedness to military standard 810F for extreme environmental conditions. “There are 15 tests we do to be sure we are completely compliant with that standard,” said Rich Perley, Augmentix vice president of marketing.
Augmentix enhanced the Dell LCD screen by encasing it in a magnesium enclosure. “It gives the screen more torsion,” Perley explained. But the company does not yet offer a touchscreen in its enhanced, rugged Dell Latitudes. “There are a lot of applications that are keyboard-centric and don’t need a touch-screen, so if you’re not going to use it, why pay for it?” he asked.
Nonetheless, Augmentix plans to expand its product offerings next year to take advantage of the growing demand. “There are really four to five segments in the rugged notebook market today, from the consumer to the emerging durables, to semi-rugged to fully rugged and at the top, ultra-rugged,” he said “And there’s definitely a market for the rugged, outdoor readable touch-screen, so we will have a touch-screen model out in six months.”
Another issue in outdoor-readable displays has been their tug on performance, although the degree to which this occurs depends on which rugged notebook is in play. “Past performance problems in some rugged laptops with outdoor displays were resolved when the new models came out with Intel Core 2 Duo processors, which provided increased performance and less consumption of power,” noted Jain.
So the performance issue has nearly vanished and could become a non-issue when quad core processors show up in the laptops of the future. For now they are only in server models, but as Walls noted, they will likely wind up in rugged notebooks with outdoor touch-screens given the military’s increasingly mobile use of rugged notebooks as servers.
Although CCFL backlights provide relatively low power consumption and bright light, some companies plan to replace current CCFL backlights with several LEDs.
In March, Toshiba Matsushita Display Technology introduced new notebook panels that incorporate an LED backlighting system with light weight and low-power consumption. Toshiba claims its LED backlighting has reduced thickness and weight compared with a conventional CCFL backlighting system. LED backlighting can also be low cost, long life, relatively immune to vibration and can provide more precise control over its intensity.
“The technology is heading toward LED and organic LED displays, so we are looking at taking DynaVue into those types of display technologies in the future,” said Thacker. ♦
