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First green LED means a lighting revolution is fast approaching

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April 8, 2010

First green LED means a lighting revolution is fast approaching

First green LED means a lighting revolution is fast approaching

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When scientists at the National Renewable Energy Laboratory (NREL) tried to apply their expertise in solar cell technology to build a green LED light from the ground up, they surprisingly centered the objective at their very first try. In doing so they solved a long-standing technological problem and paved the way for the large-scale employment of white LEDs for public and domestic illumination over the course of the next few years.

What's wrong with your good ol' tungsten bulbs, you may ask? The problem is that they produce light by incandescence, which is about the least efficient way to produce light — it wastes the majority of energy to produce useless heat, which inevitably ends up inflating your electrical bill. To a lesser extent, compact-fluorescent lights also share this inefficiency problem, which has led the U.S. Department of Energy to predict that both kinds will be phased out in the space of only four and ten years respectively, leaving LEDs virtually the only player in the market.

LED lights are unanimously regarded as a vast improvement over previous light bulbs because of their much longer lifespan and higher efficiency, which ends up saving us money in the long run, even when the higher initial cost is taken into account.

But to create a white LED, red, blue and green light need to be combined. While the first two colors have been relatively easy to manufacture, researchers have struggled to produce a green LED. The LED-based lights available today circumvent the problem by aiming the blue light at a phosphor, which then emits green light. This does produce white light, but it is still wasteful compared to a white light that makes use of three distinct, all-LED components.

NREL researcher Angelo Mascarenhas, who holds patents in solar cell technology, realized that a LED can be thought of as the reverse of a solar panel, since one takes electricity and turns it into light, while the other takes (sun)light and turns it into electricity.

Mascarenhas used the knowledge gathered by NREL when they created a world-record inverted metamorphic solar cell by combining layers of different lattice sizes to optimally capture solar energy across the visible spectrum. The researchers had already tackled the problem of how to absorb sunlight in the green spectral region, and Mascarenhas built on this knowledge to reverse the process in order to manufacture a green LED.

Absorbing green light is technically challenging because of the way the different layers of lattice that should absorb it are manufactured: if the layers don't match up with the layer below, leaving too big a gap, the efficiency plummets to next to zero. NREL's solution was essentially to insert extra layers of lattice that gradually bridge the gap, improving the cell's efficiency.

Mascarenhas's idea was to reverse the process — that is, making a current flow between appropriately spaced layers of lattice to obtain green light - and reportedly managed to produce a radiant deep green light on the very first try.

NREL is now trying to produce a fourth color to make the white light even whiter. They plan to arrange the four colors in a beehive structure, each cell being an LED of a specific color, so that the light will look white when seen from a distance.

The researchers also plan to make their LED light "intelligent," dynamically matching the percentage of the four colors to the time of the day - for instance, increasing the blue component during daylight, or the reddish-yellow during the night.

Further predictions from the Department of Energy estimate that the move toward LEDs for both public and domestic lighting could save the U.S. as much as US$120 billion over the course of the next 20 years, as well as 246 million metric tons of carbon (approx. 5 percent of U.S. total emissions during the period 1850 through 2000) that would otherwise be released into the Earth's atmosphere.

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino
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11 Comments

I thought we had had green LEDs for the last 30 years. Practical Blue ones came much later. What am I missing here

Steve Lane
9th April, 2010 @ 04:14 am PDT

Maybe I'm missing something, but haven't green LEDs been around for ages? There are three on my keyboard as I type this!

felix
9th April, 2010 @ 04:37 am PDT

Green LEDs have been around for a long time, long before the blue or UV LED, and are in common use as indicators, organic LED displays, LED displays, and in some RGB white or colour changing LED lights. They used to be of a relatively energy inefficient design, however this is definitely not the first green LED. Perhaps it is a more energy efficient design than in the past.

DH
9th April, 2010 @ 11:33 am PDT

What? There have been green LEDs for at least TWENTY YEARS. Red ones were the first, back in the late 1960's. Orange, yellow and amber came soon after.

Blue LEDs weren't perfected until the late 1990's. Very early white LEDs were made by combining red green and blue diodes in a single package, often with a pair of greens to make up for their slightly lower brightness.

For the past few years white LEDs have been produced by covering a blue diode with a yellow phosphor. The combination of the visible blue light and the wavelengths emitted by the ultra-violet excited phosphor combines to produce white light.

First green LED is way off the mark. The author needed to do a whole lot more research on the subject before starting to write this article.

Facebook User
9th April, 2010 @ 02:39 pm PDT

Is that correct? Green LEDs start as blue. I seem to recall that green LEDs were the 2nd color ever developed for LEDs, which gave us yellow LEDs. But Blue took another 25 years to be invented.

Eletruk
9th April, 2010 @ 05:46 pm PDT

Full story here at NREL website, which may clarify some of the confusion:

http://www.nrel.gov/features/20100405_leds.html

matthew.rings
11th April, 2010 @ 09:23 pm PDT

If I memory serves, Current 'Green' LED's are actually a blue led shone through a phosphor....the cheaper ones are just in a green plastic shell...

marshall91t
12th April, 2010 @ 04:50 am PDT

Nooooooooooooo I have been making GREEN LED's for at least 50 years.

Simple:

Get one diode. Paint it green. Put under light source - sunlight is best. Diode emits green light.

A green "solar powered" Light Emitting Diode.

Too easy.

Mr Stiffy
13th April, 2010 @ 06:29 pm PDT

I don't how they can have 'phosphor' in a 'clear' green LED package?

http://www.radioshack.com/product/index.jsp?productId=3104292&CAWELAID=166061612

wirelessdj
13th April, 2010 @ 06:53 pm PDT

Current Green LED are just basically Tinted Green, either through phosphor or by painting it with some cheap paint.

Basically what this guy has done is create a LED that directly creates green light, so now we finally have the last colour in light development. Red was first, since its closest to the infrared spectrum which is easiest to replicate, then I think its blue then white which I think is just a extremely bright blue or sometimes extremely bright red, so now we have the green for a 3 or has they suggested a 4 colour white, which would make it allot cheaper.

Josh1235
25th May, 2010 @ 02:07 am PDT

did any of you guys read the article, because if you did you would know that they get it today by REFLECTING blue off of 'phosphor' !!!!!!!!!!

skippyxxx
25th May, 2010 @ 10:51 am PDT
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