Cheap, efficient white light LEDs new design

Apr 07, 2009
Light produced by a new type of light emitting diode (LED) made from inexpensive, plastic-like organic materials. Photo by Ma Dongge

Roughly 20 percent of the electricity consumed worldwide is used to light homes, businesses, and other private and public spaces. Though this consumption represents a large drain on resources, it also presents a tremendous opportunity for savings. Improving the efficiency of commercially available light bulbs -- even a little -- could translate into dramatically lower energy usage if implemented widely.

In the latest issue of Journal of Applied Physics, published by the American Institute of Physics (AIP), a group of scientists at the Chinese Academy of Sciences is reporting an important step towards that goal with their development of a new type of (LED) made from inexpensive, plastic like organic materials. Designed with a simplified "tandem" structure, it can produce twice as much light as a normal LED -- including the desired for home and office lighting.

"This work is important because it is the realization of rather high efficiency white emission by a tandem structure," says Dongge Ma, who led the research with his colleagues at the Changchun Institute of Applied Chemistry at the Chinese Academy of Sciences.

Found in everything from brake lights to computer displays, LEDs are more environmentally friendly and much more efficient than other types of . Incandescent bulbs produce light by sending electricity through a thin metal filament that glows red hot. Only about five percent of the energy is turned into light, however. The rest is wasted as heat. Compact fluorescent bulbs, which send electricity through a gas inside a tube, tend to do much better. They typically turn 20 percent or more of the electricity pumped through them into light. But compact fluorescents also contain small amounts of mercury vapor, an environmental toxin.

LEDs on the other hand, are made from thin wafers of material flanked by electrodes. When an electric current is sent through the wafers, it liberates electrons from the atoms therein, leaving behind vacancies or "holes." When some of the wandering electrons and holes recombine, they create a parcel of light, or photon. These photons emerge from the side of the wafer as visible light. This turns 20 to 50 percent, or even more, of the input energy into light. LEDs also concentrate a lot of light in a small space.

Producing LEDs that can compete with traditional light bulbs for cost and efficiency is one thing. Making LEDs that consumers want to use to light their homes is quite another. One of the main barriers to the widespread use of LED lights is the light itself. LEDs can easily be manufactured to produce light of a single color -- like red -- with applications such as traffic lights and auto brake lights. Indoor lighting though, requires "natural" white light. This quality is measured by the color-rendering index (CRI), which assigns a value based on the light source's ability to reproduce the true color of the object being lit. For reading light, a CRI value of 70 or more is optimal. LEDs can produce white light by combining a mixture of blue, green, and red light, or by sending colored light through a filter or a thin layer of phosphors -- chemicals that glow with several colors when excited. However, these solutions increase costs. To reach a larger market, scientists would like to make inexpensive LEDs that can produce white light on their own.

The authors of this paper report important advances towards this goal. First, they built LEDs from organic, carbon-based materials, like plastic, rather than from more expensive semiconducting materials such as gallium, which also require more complicated manufacturing processes. Second, they demonstrated, for the first time, an organic white-light LED operating within only a single active layer, rather than several sophisticated layers. Moreover, by putting two of these single-layer LEDs together in a tandem unit, even higher efficiency is achieved. The authors report that their LED was able to achieve a CRI rating of nearly 70 -- almost good enough to read by. Progress in this area promises further reduction in the price of organic LEDs.

More information: "A high-performance tandem white organic LED combining highly effective white units and their interconnection layer" by Qi Wang et al. was published online on April 6, 2009 [J. Appl. Phys. 105, 076101 (2009)]. link.aip.org/link/?JAPIAU/105/076101/1

Source: American Institute of Physics

Explore further: Serial time-encoded amplified microscopy for ultrafast imaging based on multi-wavelength laser

add to favorites email to friend print save as pdf

Related Stories

Efficient organic LEDs a step toward better lights

Dec 23, 2008

(PhysOrg.com) -- For those who love "green" compact fluorescent bulbs but hate their cold light, here's some good news: Researchers are closer to flipping the switch on cheaper, richer LED-type room lighting.

The Green (and blue, red, and white) lights of the future

Dec 17, 2008

A revolution in energy-efficient, environmentally-sound, and powerfully-flexible lighting is coming to businesses and homes, according to a paper in latest special energy issue of Optics Express, the Optical Society's open-a ...

High-brightness breakthrough

Jun 28, 2005

As a result of cooperation between Philips Lighting, Philips Research and Novaled have announced a new record for the efficiency of high-brightness white OLEDs, a new solid state lighting technology. OLEDs are expected to ...

Recommended for you

A transistor-like amplifier for single photons

16 hours ago

Data transmission over long distances usually utilizes optical techniques via glass fibres – this ensures high speed transmission combined with low power dissipation of the signal. For quite some years ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

Soylent
2.3 / 5 (6) Apr 07, 2009
Roughly 20 percent of the electricity consumed worldwide is used to light homes, businesses, and other private and public spaces. Though this consumption represents a large drain on resources, it also presents a tremendous opportunity for savings. Improving the efficiency of commercially available light bulbs -- even a little -- could translate into dramatically lower energy usage if implemented widely.


That's just flat wrong.

Only 10% of the residential electricity consumption is lighting.

Residential electricity consumption is only one third of total consumption.

Only the residential sector is still using inefficient incandescent lighting.

The least efficient lighting is fluorescent lighting and LEDs don't significantly improve on that; never mind competing with the gas-discharge lights(especially HPS street lights).
googleplex
5 / 5 (1) Apr 08, 2009
There are other benefits beyond efficiency i.e. production cost, toxicity and Mean Time Between Failure. All of the CFLs I have used contain mercury which is Haz Mat (highly toxic). At most they last about 2 or 3 times as long as incandescent. Also if you look at the energy required to manufacture them it is high, requiring glass.
IMHO LED lights are more efficient than flourescent with even more benefits.
It wouldn't suprise me if a significant lighting solution came out of China. US Corporations making lights that last long is counter to their primary goal of profit.
Soon CFLs and Flourescents will soon become as un-popular as asbestos once they are in wide spread use. Just wait for the law suits. For some reason they have only minimal documentation on the packaging. They should have Haz Mat labels.
Mercury has an affinity for nerve tissue. Damage is permanent and currently un-treatable.
http://www.epa.gov/hg/spills/
jeffsaunders
not rated yet Apr 08, 2009
Keep working on it. If I have to try and read one more book under those small useless fluorescent lights I will go blind.

If I want to read a book in my house I have to stand under the fluorescent light in the kitchen or try and use the bathroom which still has an incandescent light in the socket.

I do have a reading lamp which uses those 12 volt lights - they are bright enough but then I have to sit under that lamp and it does get hot in summer.
googleplex
not rated yet Apr 15, 2009
Keep working on it. If I have to try and read one more book under those small useless fluorescent lights I will go blind.
If I want to read a book in my house I have to stand under the fluorescent light in the kitchen or try and use the bathroom which still has an incandescent light in the socket.
I do have a reading lamp which uses those 12 volt lights - they are bright enough but then I have to sit under that lamp and it does get hot in summer.

You should use a nice quartz halogen bulb for reading. I think they give a good spectrum of light.
Anyway why are u still reading books. I only read backlit computer screens these days.
jeffsaunders
not rated yet Apr 16, 2009
googleplex

I do not find computer screens quite as portable nor as functional as a book. When they are I will use them. till then I read a lot of stuff on the computer but not novels.