Displays market loves LED lighting

This year, the market size for high brightness (HB) LEDs is expected to reach $12bn and grow to $20.2bn by 2015. One application area driving this growth is the use of LEDs in backlight of TFT-LCDs, writes Tony Armstrong (pictured), director of product marketing for power products at Linear Technology.

Tony Armstrong Linear Tech

Applications range from high definition TVs and portable tablet PCs to automotive displays and a myriad of handheld communication devices. However, in order to maintain this impressive growth rate LEDs must not only offer enhanced reliability, reduced power consumption and more compact form factors, but they must also provide improvements in contrast ratios and color accuracy.

Furthermore, in automotive, avionic and marine displays all of these improvements must be optimized while simultaneously being subjected to a wide array of ambient lighting conditions ranging from bright sunlight to moonless nights.

These TFT-LCD applications range from infotainment systems, gauge clusters and a wide array of instrument displays. Of course, backlighting these displays with LEDs creates some unique LED driver IC design challenges in order to optimise display readability across a myriad of lighting conditions.

This requires LED drivers to offer very wide dimming ratios and high efficiency conversion while also withstanding the rigors of the relatively caustic automotive electrical and physical environment. It goes without saying that these solutions must offer very low profile, compact footprints while simultaneously enhancing overall cost-effectiveness.

But how can this impressive growth potential in automotive lighting be supported? First of all, LEDs are ten times more efficient at producing light than incandescent bulbs and almost twice as efficient as fluorescent lamps, including cold cathode fluorescent lamps (CCFL); thereby reducing the amount of electrical power required to deliver a given amount of light output (measured in lumens per watt).

As LEDs are further developed, their efficacy, or ability to produce lumens of light output from an electrical power source, will only continue to rise. Secondly, in this environmentally conscious world of ours, LED lighting does not require the handling, exposure and disposal of the toxic mercury vapor commonly found in CCFL bulbs. Finally, incandescent bulbs are usually required to be replaced after approximately 1,000 hours of operation while fluorescent bulbs can last as long as 10,000 hours. However, these figures are dwarfed in comparison to the 100,000 hour plus lifetimes afforded by LED lighting.

In most applications, this extended operating lifetime allows for LEDs to be permanently embedded into the end-application. This is especially important for the backlighting of automotive clusters, instrumentation and infotainment panels – which are often embedded into a vehicle’s dashboard, since they will not require replacement during the working life of the car.

Additionally, LEDs are orders of magnitude smaller and more compact than their counterparts so the LCD panels can be made extremely thin, thereby requiring minimal volumetric space in a vehicle’s interior. Also, by using a configuration of red, green and blue LEDs, an infinite number of colors can be delivered.

Furthermore, LEDs also have the ability to dim and turn on/off much faster than the human eye can detect, enabling significant improvements in backlighting of LCD displays while simultaneously allowing dramatic contrast ratios and a higher resolution picture.

Nevertheless, one of the biggest obstacles facing automotive lighting systems designers is how to optimize all of the features and benefits provided by this newest generation of LEDs. Since LEDs generally require an accurate and efficient current source and a means for dimming them, a LED driver IC must be designed to address these requirements under a wide variety of operating conditions.

Further, their power supply solutions must be highly efficient, rugged and reliable while also being very compact and cost effective. Arguably, one of the most demanding applications for driving LEDs will be found in the backlighting of automotive infotainment and instrument TFT-LCDs as they are subjected to the rigors of the automotive electrical environment where they must compensate for a wide variation of ambient lighting conditions and must fit in a very space constrained areas. And all the while, they must have an attractive cost structure.

Many emerging automotive designs use a single panel to backlight all of the display gauges for driver control. Often, the LED backlighting for the instrument panel is shared with the infotainment system, creating an easy to read all-in-one control panel. Similarly, many vehicles including cars, trains and airplanes also have LCD displays that entertain passengers in the rearward seat(s) with movies, video games and so forth.

Historically, these displays have used CCFL backlighting; however, it is becoming more common to replace these relatively large bulb designs with very low-profile arrays of white LEDs to provide more precise and adjustable backlighting as well as an extended service life.

In conclusion, the benefits of using LED lighting in an automotive environment has several positive implications. First, they never need to be replaced, since their solid state longetivity is in excess of 100K hours – equivalent to 11.5 service years, thereby surpassing the life of the vehicle. This allows automobile manufactures to permanently embed them into “in cabin” backlighting without requiring accessibility for replacement. Styling can also be dramatically altered as LED lighting systems do not require the depth or area as do CCFL bulbs.

And, finally, LEDs are also generally more efficient than fluorescent bulbs at delivering light output, measured in lumens/watt. This has two positive effects. First, it drains less electrical power from the automotive bus and, equally as important, it reduces the amount of heat that needs to be dissipated in the display, thus eliminating any requirement for bulky and expensive heat sinking. Yes, the future is bright indeed for LED lighting.

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