Next generation LED and OLED lighting
As my colleague Anil Duggal discussed on his latest blog entry, GE Global Research has recently won two DOE contracts for next generation LED and OLED lighting products. Apart from the work to develop OLEDs for general illumination applications, the Research Center is also developing different technologies to improve the quality and price of LED-based lighting products.One of these technologies (that I directly work on) is the invention and development of LED phosphor materials with the goal to improve both the energy efficiency and quality of light in LED lighting. Broadly speaking, typical phosphors are micron-sized ceramic powders that are doped with a small amount of optically active ions (typically a rare-earth ion) that absorb light and downconvert it into lower energy radiation.
Today, the vast majority of white LEDs combine blue LEDs and a phosphor that downconverts blue LED light into yellow light; the combination of blue and yellow radiation “mix” to make white light. This combination of blue and yellow light gives white light with a cool white color temperature (CCT>4000 K) and reasonable color rendering indices (CRI~70-80), enabling to be used in many applications where color quality is not a key requirement, including backlights for portable displays, indicators, and large-area lighting (e.g. parking lot lamps and street lights).
However, implementing LEDs in most general lighting applications requires higher color rendering and “warmer” colors. As a reference point, typical incandescent and halogen lamps have color temperatures of 2500-3100 K and a CRI defined at 100. One path to achieve LED lamps with higher CRIs is to develop additional phosphors (especially in the red spectral region) that lead to lower color temperatures and higher CRIs. An issue with current “warm white” LED packages typically have an efficacy of ~70% of comparable “cool white” LED packages. Reducing this efficacy gap motivates DOE to support phosphor development programs such as the one that we are completing and our new program that was just awarded.
There has been extensive research and development for phosphors in fluorescent lamps, cathode-ray tubes (CRTs), and x-ray films, but most traditional phosphors are not suitable for pcLEDs because many of them do not strongly absorb violet or blue LED radiation and will lead to scattering losses in LED packages. Therefore, new compositions and materials are needed, and aspects of solid-state chemistry, spectroscopy, and ceramic processing are required to develop these new LED phosphors. We have had success in our previous DOE program since we invented and developed phosphors that can potentially close the efficacy gap between “warm white” and “cool white” packages to <15% (see attached picture). In our next program with DOE, we will be taking further steps to improve the efficacy of our “warm white” packages by accounting for the specific properties of our new phosphors within the optical design of LED lamps/packages. By improving the efficacy of “warm white” LEDs, we will be accelerating their implementation into the general marketplace and save energy by replacing less efficient lamps.
As Anil pointed out in his blog entry, we are working to finalize contract details on both projects with the DOE. If you want to read more, in the future, we’ll discuss some of the exciting results from all of the folks that work on LED-based lighting and phosphors. As well you can check out this piece that just hit in Popular Mechanics magazine over here. Stay tuned!
