34377\Sharp WP high brightness displays

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As bright as daylight - but dark at night

High brightness LED backlit TFT LCDs combine high performance and extensive brightness control to ensure that displays remain perfectly easy to read under all ambient light conditions - an absolute must for certain applications.

Electronic nautical chart tables are perhaps the best example of just how important the combination of high display brightness and the extensive adjustability of backlighting can be.

On both large cargo ships with several thousand gross register tons and agile sport boats and yachts, nautical maps must be easy to read in all weather and light conditions. This means that a high level of display brightness is required during the daytime, so that the chart plotter remains easy to read on ship bridges with a large number of windows, whilst at night the screen has to be darkened to a minimum; for safety reasons, in fact, it must neither dazzle the skipper nor obstruct vision due to window reflections.

Ultimately the most important aspect for electronic chart plotters is also relevant to all applications which are exposed frequently to wide variations in light conditions. These include all systems which are used in outdoor or semi-outdoor areas, such as e-kiosk systems, vending machines, information terminals and e-signage monitors, as well as portable test and measuring devices or control units for agricultural, forest and construction machinery.

In conditions of direct sunlight, depending on their size and location, displays generally require around 1200 cd/m² for good visibility of the screen contents, whilst in cloudy conditions, even half this level of brightness is sufficient. At night on the other hand, 250 cd/m² is perfectly adequate - in a darker environment, greater brightness can in fact lead to dazzling effects and disturbing reflections.

LED backlights - easy to dim, economical and sturdy

Wherever it is important to be able to adjust display brightness, LED backlit TFT LCDs generally have a lead over conventional screens with CCFL backlighting. In technological terms, cold cathode lamps can only be dimmed to a limited extent. LEDs are different: due to their physical structure and extremely rapid response characteristics, their brightness can be adjusted continuously from zero to the maximum value. Digital adjustment via pulse-width modulation is preferred in this case, the brightness level being the result of the length of the voltage pulses.

One positive side effect of the good dimmability of LED backlighting is enhanced energy efficiency with optimal display illumination. In contrast to CCFL backlights, LEDs can easily be

readjusted in relation to the ambient lighting, producing the same level of brightness with a consumption of around half the energy. Accordingly, the power consumption is reduced to around a fifth at night, compared to a full load on sunny days.

Also with regard to mechanical resistance, LEDs are a step ahead as backlighting source.

From their quality alone, they are considerably less sensitive to impact and vibrations than the glass bodies of CCFLs. In addition to this, LEDs can work with a low-voltage power supply. The omission of high-voltage converters reduces the complexity of the entire display module, whereby LED backlights are considerably less sensitive to mechanical loads.

High-brightness displays with power reserves for all light conditions

For outdoor and semi-outdoor areas in which applications are exposed to strongly and rapidly fluctuating light conditions, Sharp offers a range of High Brightness TFT LCDs with diagonals of 12.1" to 23.1". With a display brightness of up to 1200 cd/m², they offer sufficient lighting reserves to ensure good readability even in very bright daylight and direct sunlight. Thanks to the LED backlighting, on the other hand, the display brightness can be easily dimmed appropriately in a darker environment. The extremely bright backlights are also an advantage when displays - as is often the case with e-kiosk applications, vending machines and ATMs and interactive information terminals - are equipped with touch-screens.

By installing the touch-sensitive, additional layer, the original brightness of the LCD module is reduced by around ten per cent.

The new series of High Brightness LCDs from Sharp include, amongst other models, the

LQ190E1LX51 type 19" SXGA display, which provides a brightness of up to 1,000 cd/m² with a contrast ratio of 900:1 and a viewing angle of 170°. For easy dimmability to control the display brightness, the drives for PWM dimming are already integrated features of the

LQ190E1LX51. In addition to the classic industrial applications, it is also perfectly suitable for e-kiosk applications, for example, which are now frequently used in both semi-outdoor and certainly in outdoor areas.

The LQ231U1LW32 type 23" UXGA display, also new, offers a display brightness of up to

500 cd/m², a contrast ratio of 600:1 and also a viewing angle of 170°. This product is also used in electronic nautical chart tables in ships, for example. In order to easily create a dimming feature for night-time use, the LQ231U1LW32 is also fitted with a driver for PWM dimming directly on board.

The LQ121X3LG02 type 12.1" XGA display was already presented by Sharp in the middle of last year. It stands out due to its display brightness of up to 1,200 cd/m² and a contrast ratio of 1000:1.

The new high-brightness LCD modules from Sharp also stand out in terms of sturdy construction and mechanical resistance. In both switched-on and -off mode, the 19" LCD is able to withstand accelerations of up to 19.6m/s² in a standard vibration test in the range of 57 –

500 kHz. In a standard impact test, in operating mode it is able to withstand impacts with acceleration values of up to 294 m/s² without damage.

The 23" LCD also scores well in this area. In the vibration test in the range of 57 - 500 kHz, it is able to withstand accelerations of up to 9.8 m/s² and impacts with acceleration values of up to 147 m/s² in the standard impact test.

All three display models operate at temperatures ranging from -20 to +60 degrees Celsius and can therefore be used equally on hot summer days as well as on cold winter days.

With a service life of at least 50,000 hours and long-term product availability, Sharp offers its customers displays which are optimal for outdoor use and, naturally, at the same time ideally suited for both industrial and indoor applications.

Temperature management: a challenge

The challenge posed by the integration of LED backlighting in industrial displays is and remains that of temperature management. Unlike displays specified for CE devices, which are operated at room temperature and only for a few hours a day, industrial displays are often operated on a continuous basis at temperatures of -20 to 60 degrees Celsius. This represents a challenge, especially at the higher end of the temperature scale. At higher temperatures

LEDs are sensitive. A strong local heat build-up on the lighting modules must be discharged effectively, as it can damage the LCD panel and the backlighting itself, which would lead to a significant reduction in service life. For this reason, Sharp has developed a special chassis for LED backlit industrial displays, in which the LEDs of the backlighting are thermally coupled directly to the mechanical parts of the module. In this process, the chassis acts both as a heat sink which efficiently discharges waste heat into the environment via the rear of the display, ensuring that there is no damaging heat build-up even at high ambient temperatures.

In technological terms, LEDs are far superior to CCFLs at low temperatures; at ambient temperatures under 0°C, LED backlights can in some cases reach a service life of 200,000 hours. In addition, LEDs can reach full light output the moment they are switched on, whilst

users require a certain amount of patience in the case of CCFLs, especially at low temperatures.

Summary:

For outdoor use, TFT LCDs require a whole series of properties: high sturdiness, temperature adaptability and a long service life - something taken for granted in the case of many industrial LCDs. To ensure optimal readability under frequently changing light conditions, however, LED backlighting solutions are indispensable as, unlike cold cathode lamps, they offer the full dimmability required to ensure flexible control of the display brightness. The high brightness industrial LCDs offered by Sharp also have sufficient power reserves to ensure good readability even in bright sunlight.

Selection must be made with care, however: In technological terms, LED backlights require specific heat dissipation, as heat build-ups can shorten the service life of the display, in particular under high ambient temperatures. For this reason, Sharp has developed a patented solution for LED backlit industrial LCDs, in which the display housing also acts as a heat sink.

Box: Experts are asked about the industrial suitability of LED backlights.

Why are LED backlights catching on for industrial displays only now, although they have been a common feature in LCD TVs for a long time already?

Displays suitable for industrial use are subject to very different requirements, with regard mainly to thermal resistance and daily running time. CE are generally designed for operation at room temperature for between 3-4 hours per day. Screens used in industrial environments must withstand ambient temperatures reaching as high as 60°C, sometimes for 24 hours per day. Especially at such high operating temperatures, CCFLs were even more suitable until recently. Due to the increasing energy efficiency and the ensuing lower waste heat of LEDs on the one hand, and the special chassis design developed by Sharp on the other hand, LEDs can now be used for the backlighting of industrial LCDs without compromising on the service life.

How do LED backlights perform at extremely cold temperatures?

In frosty conditions, LEDs were always one step ahead. They reach full brightness when connected to the supply voltage, whilst CCFLs first have to "warm up" before they reach their

full potential, which can sometimes take a few minutes. Compared to CCFLs, cold temperatures can also lengthen the service life of LEDs up to 200,000 hours at temperatures below

0°C. Apart from the above, LEDs are also more sturdy than CCFLs with their glass bodies with regard to mechanical strain.

In very general terms, how do LED backlighting systems alter the design of human-machine interfaces?

Until now, the design of human-machine interfaces was always geared towards obtaining the maximum display brightness required, as dimming CCFLs shortens their service life.

Thanks to the new generation of industrial LED backlit LCDs, development engineers now have greater flexibility and can specify default settings for display brightness for example based at half of the backlit power output, without shortening the service life. This means that there are still sufficient reserves to readjust the display brightness accordingly under very bright or dark ambient light conditions. Such situations frequently occur in applications such as e-kiosk systems and information terminals located outdoors or in semi-outdoor areas. Specifically for these applications, Sharp is also planning high brightness, LED backlit displays which are efficient even in sunlight, but can also be used easily under normal light conditions in half-light, without this impairing the backlighting. Sharp supports these new design concepts and has already fitted the new high brightness LCDs with drivers for pulse-wide modulation dimming.

Specifications:

Display size

Resolution

Dimensions (wxhxd)

Luminance

Contrast

Colours

LQ121X3LG02 LQ0190E1LX51 LQ0190E1LX51

12.1 inch / 31 cm 19 inch / 48 cm 23.1 inch / 59 cm

1024 x RGB x

768

259 x 205 x 7.5 mm

1200 cd/m²

1000:1

262144 / 18-bit

1280 x RGB x

1024

404.2 x 330 x 34 mm

1000 cd/m²

900:1

1600 x RGB x

1200

530 x 431.5 x

23.9 mm

500 cd/m²

600:1

16 million / 24-bit 16 million / 24-bit

Temperature range -20 – +60°C -20 – +60°C -20 – +60°C

Interface

Service life (h)

Special features

Supply voltage

LVDS

50000

-

3.3V

LVDS

50000

PWM Dimming

5 V

LVDS

50000

PWM Dimming

5 V

Availability immediately immediately immediately

Author:

Gunter Wagschal

Project Manager Business Unit Industrial

Sharp Microelectronics Europe

Sonninstraße 3

20097 Hamburg

Telephone: +49 (0)180 507 35 07 (EUR 0.14

/min. from the landline network of DTAG.)

E-mail: [email protected]

Web: www.sharpsme.com

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