Backlight assemblies less than 1 mm high utilizing light-guides as thin as 0.4 mm are now a reality thanks to new backlight units (BLUs) from Global Lighting Technologies. The components are designed to offer the thinness of electroluminescent backlighting, with the advantages of advanced LEDs and superior light extraction provided by injection-molded light-guides.
Global Lighting Technologies (GLT, www.glthome.com) of Brecksville, OH, U.S. has introduced new LED-based backlights that offer measurements as low as 0.4 mm, providing what the company claims to be the thinnest molded light-guide backlight units (BLUs) available. Designed to backlight today’s ever-slimming consumer electronics, the light-guide package is not only thin, but is said to be efficient as well.
David DeAgazio, director of sales, says offering engineers this type of package requires careful design. “Typically, as light-guides become thinner, the efficiency of the light-guide will decrease,” he explains. “This is due to the total internal reflection (TIR) of light inside the light-guide. The thinner the light-guide, the faster the light ‘bounces’ inside the light-guide, and the harder it gets to precisely extract light and provide uniform light to the far end of the light-guide.”
The company’s patented MicroLens light extraction technology allows GLT engineers to have control over variables such as size, shape, depth, pitch, and angle of rotation, which DeAgazio says is the key to achieving small size and efficiency. “Unlike other ‘thin’ light-guides that use a secondary printed process, the MicroLens features are molded directly into the light-guide, thereby reducing cost,” he notes.
DeAgazio says improved proprietary software, new fabrication equipment and tooling, and smaller LEDs also played a role in developing the new BLUs. “It is important to note that for optimal coupling efficiency, the thickness of the light-guide should be no thinner than the height of the LED,” he explains. “This means that if the LED height is 0.6 mm, the light-guide should be no thinner than 0.6 mm. If the light-guide were thinner, you would have uncontrolled light from the LED shining over and/or under the light-guide.”
While it is possible to “ramp” the light-guide to make it locally thicker near the LED, DeAgazio says this does not allow for optimal efficiency. “Today’s thinnest production LEDs are in the 0.4-mm range. This, along with MicroLens [technology], has enabled the thinner backlights.”
The new components are ideal for slim consumer electronics such as mobile phones, laptops, and MP3 players. Because MicroLens technology extracts light exactly where it is needed, the BLUs can also be used around through-holes for keypads in smart phones and PDAs. “They have been proven in applications ranging from 0.25-in. (diagonal) backlights to our latest backlights for 46-in. LCD TVs,” DeAgazio says. “When it comes to appliance designers, high-efficiency backlights can mean fewer LEDs (less complexity, less cost), or maybe the same number of LEDs with higher brightness, or the same brightness with lower power. It all depends upon what the designer considers most important.”