Propeller Headed: Polarized LEDs

Okay, today’s item is not a little technical; it’s a lot technical. But as always, I’ll not only tell you the story, but also what it means. So hang in with me on this one….

At the end of last month, Rensselaer Polytechnic Institute issued a press release about Martin Schubert, a doctoral student in engineering, who has been awarded the $30,000 Lemelson-Rensselaer Student Prize. So what did Martin Schubert discover that earned him this prize? He has invented a new type of LED (the inorganic type, not the Organic LEDs that are being investigated as a new display panel technology). These new LEDs have one peculiar and valuable trait; they produce polarized light. Apparently, Schuber discovered that all LEDs produce polarized light to some degree, but were not optimized for this feature. He discovered a way to maximize the effect.

What is polarized light? Light behaves like waves, but unlike waves on the ocean that only go up and down, light can “wiggle” in any direction. Polarizing films are like setting up an iron railing fence and flinging plates at it. Only plates lined up vertically will go through; all others will be blocked. This is why polarized lenses in sunglasses cut down on glare. They only let light through whose waves are oriented in one direction, and block all the others.

So why should you care? Polarized light is essential for LCD displays. The liquid crystal material rotates the polarize light so that it is transmitted or blocked by a top polarizing layer. But for this to work, it needs a source of polarized light. Traditionally, this is achieved by putting a polarizing layer behind the liquid crystal layer. Like the iron fence and the plates, most of the light gets blocked, and only the waves in the right angle get through. This is part of the reason that 95% of the light from a typical LCD backlight is blocked, even when the panel is showing an all white image.

Schubert’s discovery could mean that the LEDs could be used to create an LCD backlight that does not require a polarizing filter before the liquid crystal layer. This could result in more efficient and effective backlights that would require less energy and would make a more vivid image on the panel.

It will likely be years before this technology appears in commercial products, but it’s an intriguing advance that could help LCD maintain its dominance in flat panel displays.