Electronic Design

Backlight LEDs Promise A Bright Future At SID Conference

The most power-hungry component in the average laptop is the cold-cathode fluorescent (CCFL) backlight for the display. I had heard that CCFLs were on their way out, though, and that their exemption from the European Union's Restrictions on Hazardous Substances was subject to regular review.

But I'd also heard that their demise was a few years away, since LED diffusers just weren't ready for prime time yet. Stopping by some of the smaller booths at the recent Society for Information Display (SID) conference in San Francisco persuaded me that the day of the LED is coming faster than I expected.

Backlighting is important to a power editor for two reasons. First, it takes some of the pressure off the engineers who have to design laptop ac-dc converters. Second, it simplifies the task of powering backlights. Today, most new LED drivers target cell-phone applications. But I expect to see more and more higher-current drivers designed for backlights.

Part of the challenge in backlight design is the lamps themselves. Yet the real challenge lies in distributing the light evenly across a wide area. Considering this, two announcements at the SID conference impressed me the most.

The first announcement was at the Global Lighting Technologies booth. GLT had combined its MicroLens light guides with Luminus Devices' PhlatLight technology to demonstrate a 24-in. working prototype of a MicroLens/PhlatLight edge-lit LCD TV backlight. The MicroLens concept is based on the distribution of prisms in each light pipe (see the figure). Prism density is inversely related to the distribution of light intensity along the pipe.

PhlatLight (Photonic Lattice) technology, developed by Luminus Devices based on research done at the Massachusetts Institute of Technology, enables an entirely new type of solid-state light source based on patented photonic lattice structures. It's the world's first solid-state light source powerful enough to illuminate large-screen televisions and other high-definition displays.

As Luminus explains it, the concept involves suppressing "the lateral propagation of photons inside the semiconductor device." It's based on the application of photonic lattices, which are interlocking tiny slivers of silicon into a regular 3D lattice so that it has crystal-like refracting properties at a somewhat coarser scale than an actual crystal.

According to Sandia Labs, photonic lattices "form a cage that trap and guide approximately 95% of the light sent within them, as compared with approximately 30% for conventional waveguides, and they take only one-tenth to one-fifth the space to bend the light."

At another SID booth, Apollo Display Technologies demonstrated some LED-backlit display products that, while smaller than what's promised by GTL and Luminus, are actually appearing in prime time. Apollo is a distributor for LCD manufacturer Optrex, whose panels for embedded applications can be backlighted either by CCFLs or LEDs. (On the show floor, it was nearly impossible to tell the difference.)

To that, Apollo adds some video controllers that make life exceptionally easy for developers. The one I found most interesting was the ArtistaUSB Controller series, which makes it possible to drive thin-film-transistor (TFT) displays via a USB interface without the need for a graphics card. Even four-wire resistive touchscreens can be controlled via the same card.

Various graphics drivers allow the controller to run displays just like standard monitors under Windows. The controller is installed as a virtual graphics card in software form under Windows (or as a "frame buffer device" under Linux) and uses a part of the random access memory as video memory. Prices vary by configuration.

Global Lighting Technologies www.gtlhome.com
Luminus Devices www.luminus.com
Apollo Display Technologies www.apollodisplays.com

TAGS: Components
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