Display Technology I Industrial Applications As bright as day - but dark as night Power reserves
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
High brightness LED backlit TFT LCDs combine performance and brightness control to ensure displays remain perfectly easy to read under all conditions - an absolute must for certain applications, as Gunter Wagschal explains
E
lectronic 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. From large cargo ships to agile sport boats and yachts, nautical maps need to 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, whilst at night the screen has to be darkened to a minimum; for safety reasons, in fact, it must neither dazzle nor obstruct vision due to window reflections. These aspects are 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
10 October 2011
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
cd/m2 is
perfectly adequate - in a darker environment, greater brightness can in fact lead to dazzling effects and disturbing reflections.
LED backlights 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
Components in Electronics
www.cieonline.co.uk
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.
For outdoor and semi-outdoor areas in which applications are exposed to strongly and rapidly fluctuating light conditions, there are a broad range of High Brightness TFT LCDs with diagonals of between 12.1" to 23.1" that are available on the market. 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 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 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.
Temperature management 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
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