Researchers create LED that produces warm white light from a single phosphor
January 21, 2013
Researchers at the University of Georgia (UGA) have come up with a solution to the cold, bluish look of white LED (light-emitting diode) lights currently available. By creating a new lighting-emitting material, or phosphor, the researchers claim to have developed what could be the world's first LED that produces a warm white light from a single source of emission.
Current methods try to deal with the cold light issue by combining different types of light-emitting materials. The variety of materials means achieving the right combination ratio is a difficult and expensive task. As a consequence, the result is not always ideal since each of the materials in the combination can respond differently to temperature variations, and color stability is affected.
The UGA team managed to overcome these problems by combining very small quantities of europium oxide with aluminum oxide, barium oxide and graphite powders. The process involves heating those materials in a tube furnace at a temperature of 1,450° C (2,642° F). The materials then vaporize while the force of the furnace’s vacuum pulls them onto a substrate, where they are deposited as a yellow phosphorescent material. Once this luminous compound is encapsulated in a bulb and receives the light from a blue LED chip, the resulting light will be warm and white.
Led by physics professor Zhengwei Pan from UGA’s Franklin College of Arts and Sciences and the College of Engineering, the researchers say their solution meets the industry’s thresholds that indicate the indoor lighting quality. It features a color temperature of less than 4,000 kelvins (the ideal for indoor lighting) and a color rendering index of 85, (80 is the minimum value required to replicate natural light while lower values result in colors that appear artificial and unattractive to human perception).
"Right now, white LEDs are mainly used in flashlights and in automotive lamps, but they give off a bluish, cool light that people tend to dislike, especially in indoor lighting," said Pan. "Our material achieves a warm color temperature while at the same time giving highly accurate color rendition, which is something no single-phosphor-converted LED has ever been shown to do."
The researchers will now work on overcoming hurdles such as low efficiency. To do that, they need to find out how the ions in the compound are arranged so they can better understand it at an atomic level. Scaling up production will also be challenging since the material is very sensitive to temperature and pressure variations during its synthesis process, which can end up producing different colors.
LEDs are considered to be a more environmentally friendly option than incandescent lights due to their longevity and low energy consumption. However, they need to be disposed of carefully because of some toxic materials they contain.
The material is described in a paper published in the journal Light: Science and Applications.