Display Technology I Industrial Applications Q&A
SELECTING LED BACKLIGHTS FOR INDUSTRIAL APPLICATIONS
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
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 development of special chassis, on the other, 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.
moment they are switched on, whilst users require a certain amount of patience in the case of CCFLs, especially at low temperatures.
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.
Sharp Electronics |
www.sharp.eu Gunter Wagschal is a Project Manager at Sharp Microelectronics Europe
www.cieonline.co.uk
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 developing a number of 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.
Components in Electronics October 2011 11
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