Building a Better Light

Researchers working across the country have designed organic light-emitting diodes (OLEDs) that have the potential for virtually 100% efficiency, according to a recent article in Nature.

Lighting accounts for 22% of electricity consumed in United States buildings and 40% of that is eaten up by inefficient incandescent bulbs. Incandescent bulbs, though an ingenious invention, uses up a lot of the electrical energy in generating heat. Florescent lightbulbs are much more efficient, but they are costly to produce.

Light-emitting diodes (LEDs) are used in Christmas tree lights, bicycle lamps, and are becoming the preferred lighting for traffic lights across the country (where they are laid out in a circular grid pattern). They are efficient and good at generating bright point sources of light, but at present they don't generate enough light to be practical for illumination of buildings.

Typically, white-light LEDs are composed of a mixture of phosphors that produce a combination of blue, red, and green light to create white light. The blue phosphors, however, degrade quickly relative to the other colors.

The newly re-designed carbon-based LEDs use a long-lived fluorescent material to generate the blue light. Electrons interact slightly differently between fluorescent and phosphorescent materials, so the researchers moved the cathode (where the electricity starts moving through the material) and the blue fluorescing material closer together, so it can catch more of the electrons as they begin moving through the materials. The green and red phosphors would be a few nanometers further into the device, allowing it to utilize the electrons that remain excited longer. Theoretically, these LEDs could utilize virtually all of the electrons, resulting in almost 100% internal efficiency. In the lab already, OLEDs generate approximately 66% more lumens per watt than a 100-watt incandescent bulb.

These white OLEDs are versatile and could be mounted on glass and flexible plastics, but they would require a moisture barrier that, at the moment, becomes expensive. Still, with a lifetime of 10,000 hours (compared to the 1,000 hours of incandescent bulbs and 20,000 hours of fluroscent lamps) at greater energy efficiency, it is an innovation that certainly has potential.