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Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page A B E F M aG S The biggest lighting industry forum in Asia 9 – 12 June 2009 China Import and Export Fair Pazhou Complex Guangzhou, China Show highlights: • Asia’s largest lighting exhibition and the 2nd largest in the world • Over 1,500 exhibitors and 48,000 expected visitors • Over 100,000 gross sqm exhibition space • Dozens of symposiums featuring global speakers For free admission, register online now at www.light-building.messefrankfurt.com and click on Guangzhou International Lighting Exhibition For information, please contact: Tel +852 2238 9964 Fax +852 2598 8771 LBguangzhou@hongkong.messefrankfurt.com www.light-building.messefrankfurt.com Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page A B E F M aG S
Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page A B E F M aG S optical modeling | PHOSPHOR LEDs Software predicts performance of phosphor down-converted white LED designs Predictive modeling benefi ts from sophisticated algorithms and accurately measured data inputs, writes CHAO-HSI TSAO, EDWARD FRENIERE and LINDA SMITH. The use of white LEDs for solid-state lighting to address applications in the automotive, architectural and general illumination markets is just emerging. LEDs promise greater energy efficiency and lower maintenance costs. However, there is a significant amount of design and cost optimization to be done while companies continue to improve semiconductor manufacturing processes and begin to apply more efficient and better color rendering luminescent materials such as phosphor and quantum dot nanomaterials. In the last decade, accurate and predictive opto-mechanical software modeling has enabled adherence to performance, consistency, cost and aesthetic criteria without the cost and time associated with iterative hardware prototyping. More sophisticated models that include simulation of optical phenomenon, such as luminescence, promise to yield designs that are more predictive — giving design engineers and materials scientists more control over the design process to quickly reach optimum performance, manufacturability and cost criteria. White LED designs There are generally two types of white LED design forms: 1) luminescent materials including phosphors or quantum dots mounted on an LED and 2) three LEDs of primary colors combined. The TracePro Fluorescence Property Editor Utility was developed to facilitate selection of the phosphor formulation and excitation LED in design form 1) above. The earliest and most common commercially available design of this FIG. 1. Relative emission spectrum of YAG:Ce mapped to chromaticity coordinates. CHAO-HSI TSAO is the general manager and EDWARD FRENIERE is the president of Lambda Research Corp. (www.lambdares.com), Littleton, MA, and LINDA SMITH is the principal of Ceres (www.cerescom.net), Needham, MA, USA. form is a blue LED chip exciting a yellow YAG:Ce phosphor. Other designs of this type include red and green phosphors applied to a blue LED, a combination of two or more phosphors spanning blue to red applied to a UV or violet LED, and luminescent quantum dots applied to LEDs. Performance criteria include luminous flux, relative spectral power distribution, angular intensity distribution and viewing angle. Color criteria include CIE chromaticity coordinates (x, y) and correlated color temperature (CCT). Used to specify white light, CCT is a comparison of chromaticity coordinates with that of a black body. It is the temperature that corresponds to the blackbody whose chromaticity is represented by the point where the iso-temperature line from the white LED source point intersects the black body curve. Representative CCT values for commercially available white LEDs are 4500-10,000 K for cool white, 3500-4500K for neutral white, and 2670-3500K for warm white. Optimum phosphor downconversion As a simple example, consider a YAG:Ce phosphor excited by a blue LED. The formulation of the specific down-converting phosphor materials and selection of the excitation LED may be modeled and analyzed for desired color criteria using software such as TracePro’s Fluorescence Property Utility. Most often, the optical properties of existing phosphor luminescent material formulations are proprietary. However, with the goal of discovering an optimum formulation for a particular application, the user can directly import specifications from a phosphor manufacturer’s datasheet to the software as a LEDsmagazine.com JANUARY/FEBRUARY 2009 37 Previous Page | Contents | Zoom in | Zoom out | Front Cover | Search Issue | Next Page A B E F M aG S
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