LEDs - The Future Of Lighting  

New Scientist has an article on a new technique for making white LEDs that produce a more natural looking colour.

Topping LEDs with a coating of carefully tuned nanocrystals makes their light warmer and less clinical, a new study shows. The researchers argue this is a must for energy-efficient LED lights to make headway in the commercial market.

Illuminating buildings accounts for about a quarter of the electricity used in the US, according to the Department of Energy. Because most of that electricity comes from coal-fired power plants, lights account for a significant amount of greenhouse gas emissions.

LEDs have the potential to be far more efficient than other lights, but face two major hurdles. Firstly, they trail behind fluorescent lights for efficiency and, secondly, the colour of typical commercial LEDs isn't pure white.

Most emit a "cool" light with a bluish tinge, sometimes called "lunar white", that most people find unattractive in the home. Now researchers have used nanocrystals to create LEDs that give off a warm white light.

Their LEDs have a high "colour rendering index" of more than 80 out of 100, meaning objects will tend to appear their usual colour under the light. That is similar to the best fluorescent lights, but behind incandescent bulbs which define the index with a benchmark of 100.

To accomplish this, Hilmi Volkan Demir and colleagues at Bilkent University in Ankara, Turkey, coated blue LEDs with a layer of nanocrystals. These crystals are made from a core of cadmium selenide with a surrounding layer of zinc sulphide.

The crystals absorb some of the LED's blue output and emit their own red and green light. That combines with the remaining blue light to produce a soft white glow.

Existing commercial white LEDs are also based on blue LEDs. But they use a phosphor coating that converts some blue light into a broad spectrum of yellow light. When mixed with remaining blue light the result is a harsh blue-hued white.

In recent years, light emitting diodes (LEDs) have begun to change the way we see the world. Now, a Rensselaer Polytechnic Institute student has developed a new type of LED that could allow for their widespread use as light sources for liquid crystal displays (LCDs) on everything from televisions and computers to cell phones and cameras.

Martin Schubert, a doctoral student in electrical, computer, and systems engineering, has developed the first polarized LED, an innovation that could vastly improve LCD screens, conserve energy, and usher in the next generation of ultra-efficient LEDs. Schubert’s innovation has earned him the $30,000 Lemelson-Rensselaer Student Prize. ...

Schubert’s polarized LED advances current LED technology in its ability to better control the direction and polarization of the light being emitted. With better control over the light, less energy is wasted producing scattered light, allowing more light to reach its desired location. This makes the polarized LED perfectly suited as a backlighting unit for any kind of LCD, according to Schubert. Its focused light will produce images on the display that are more colorful, vibrant, and lifelike, with no motion artifacts.

Schubert first discovered that traditional LEDs actually produce polarized light, but existing LEDs did not capitalize on the light’s polarization. Armed with this information, he devised an optics setup around the LED chip to enhance the polarization, creating the first polarized LED.

The invention could advance the effort to combine the power and environmental soundness of LEDs with the beauty and clarity of LCDs. Schubert expects that his polarized LED could quickly become commonplace in televisions and monitors around the world, replacing widely used fluorescent lights that are less efficient and laden with mercury. His innovation also could be used for street lighting, high-contrast imaging, sensing, and free-space optics, he said.