LEDs are the future of video, home lighting, and more.

Christmas tree lights. Not sure if there's a politically correct way of saying that. After all, they're lights to go on Christmas trees. Festivus lights? Starting in late November and all through December (and in some places, January and February) these seemingly simple strings of lights appear draped on houses, trees, and anything else that will support them. Believe it or not, many of these lights represent a key shift in lighting technology that affects not just festive decorations, but the very heart of your television, the light in your home, and more.

What you may have noticed is a shift from the familiar and pleasant – if not slightly pastel – shades of red, green, blue, and warm white. Recent years there have been a few houses whose Christmas lights are RED, GREEN, and BLUE¸ the richness of which is unlike any other lights you've ever seen.

These are no doubt LEDs, and give you an example of what is possible with light emitting diodes.

Light-Emitting Diodes

LEDs are tiny devices that you've probably seen for years. Look at the front of your remote control—those are LEDs. Without getting too heavy into the science, they create light by putting current through a material that emits light at a certain wavelength. Different materials (or combinations of materials) emit different wavelengths. Each wavelength in this case means a different color.

So after years of research, there are now red, green, and blue LEDs. Each of these colors is available in different shades. Combining the materials in them results in new colors as well.

Coating an LED with a phosphor (a material that glows when exposed to energy) can create even more colors. The LEDs on the Samsung LN46A950 LCD are done in this way. Typically "white" LEDs are actually blue LEDs with a yellow phosphor, creating a white looking light.

Hurdles

While LEDs themselves have been around for a while, it was only recently that several significant hurdles were overcome to allow them to really push into the lighting market.

Brightness was an issue. In order to be the light source for a TV (or for other lighting uses we'll talk about later) they needed to get a lot brighter than they were.

As the saying goes, though, "the candle that burns twice as bright lasts half as long." Longevity was another issue. All lighting sources age over time, and getting LEDs to last as long as (or nearly as long as) other light sources continues to be a main objective of research. Red and green LEDs, found on electronic equipment for quite some time, have respectable longevity. Blue LEDs, which are fairly new in the LED world, have only recently achieved lifetimes similar to their red and green counterparts, still they lag behind in this regard.

And of course, there is the issue of price. LEDs aren't cheap, as the prices of the two LED backlighted LCDs in this issue show. But the prices are dropping, and as more and more products use them, the prices will drop even further.

I want LEDs!

Some of the first instances of LEDs as a TV light source were found in RPTVs, Samsung’s probably being the most recognizable. In RPTVs the LEDs served two functions. The first was to replace the UHP lamp that created all the light.

These lamps, though bright, only lasted 3,000-6,000 hours before they needed to be replaced. LEDs could last tens of thousands of hours, essentially the lifespan of the TV itself.

The second function was to negate the need for a color wheel. Single chip DLP based TVs (as nearly all RPTVs now are) create only one color at a time. Flashing each color sequentially creates all the colors you see on screen.

Your brain blurs them together. This is done with a spinning color wheel.

The color wheel, though, absorbs a lot of the light from the UHP lamp. It also causes "rainbows," or color smearing, for some viewers. LEDs (individual red, green, and blue LEDs in this case) flash their colors at a much faster rate than the color wheel could spin, so the "rainbows" aren't an issue.

While a color wheel-less light engine is technically more efficient, currently the LEDs can't match the tremendous light output of a UHP based design. With the RPTV market slowly disappearing, it's unlikely we'll see a revolution on this front. Front projectors on the other hand, offer a different avenue.

Recently, LEDs have started to find their way into the front projector market… sort of. Front projectors generally use the same type of lamps as RPTVs (some use other types of lamps, but the idea is the same). So DLP based front projectors reap the same benefits as rear projectors.

At CES this year, Vivitek and Delta Electronics both announced 1080p projectors for the home market. As we learn more about these projectors, we'll let you know.

In addition, there is a whole new category of projectors amusingly called "pico projectors" or less amusingly "pocket projectors." These devices, barely larger than a cell phone, are designed for the road warrior sales person to keep in their briefcase and do presentations on a wall in an office or other small space.

And how about a projector in your actual cell phone? That’s on the horizon too.

On to Local Dimming LCDs, home lighting, and more...