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White LEDs (white + led)

Distribution by Scientific Domains

Polymers and Materials Science	40%

Selected Abstracts

Present Status of Energy Saving Technologies and Future Prospect in White LED Lighting

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 1 2008
Tsunemasa Taguchi Member
Abstract This paper describes the present status and future prospects on the efficient energy-saving lighting system based on white light-emitting diodes (LEDs) technologies. Three types of white LEDs are introduced in terms of the fundamental lighting properties which are related to the improvement in luminous efficacy and color rendering. Practical applications using the efficient white LED lighting system are demonstrated. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

A Novel Narrow Band Red-Emitting Phosphor for White Light Emitting Diodes

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2009
Sivakumar Vaidyanathan
Research on down conversion phosphor materials is the key for the development of solid-state lighting (SSL). Especially finding alternative red phosphor for white light emitting diodes (LEDs) based on blue or near ultraviolet (NUV) LEDs is important research task. In this view, we have synthesized a series of Eu3+ -substituted La2W2,xMoxO9 (x=0,2, in step of 0.3) red phosphor and characterized by X-ray diffraction (XRD) and photoluminescence. XRD results reveal a phase transition from triclinic to cubic structure for x>0.2. All the compositions show broad charge transfer (CT) band due to CT from oxygen to tungsten/molybdenum and red emission due to Eu3+ ions. Select compositions show high red emission intensity compared with the commercial red phosphor under NUV/blue ray excitation. Hence, this candidate can be a possible red phosphor for white LEDs. [source]

A Potential Red-Emitting Phosphor BaGd2(MoO4)4:Eu3+ for Near-UV White LED

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2009
Chongfeng Guo
Red-emitting phosphor BaGd2,xEux(MoO4)4 has been successfully synthesized by a simple sol,gel method. The process of phosphor formation is characterized by thermogravimetric-differential thermal analysis and X-ray diffraction. Field-emission scanning electronic microscopy is used to characterize the size and the shape of the phosphor particles. Photo-luminescent property of the phosphor is also performed at the room temperature. The effects of firing temperature and Eu3+ activator concentration on the photoluminescence (PL) properties are elaborated in detail. PL characterization reveals that the sample with the firing temperature at 800°C and the concentration of Eu3+ at 0.7 shows the most intense emission, and its intensity is about three times stronger than that of phosphor prepared by solid-state method with the same composition and firing temperature. The new red-emitting phosphor shows an intense absorption at 396 nm, which matches well with commercial near-UV light-emitting diode (LED) chips, therefore, it is a good candidate of red phosphor used for near-UV white LEDs. [source]

Performance of high-power III-nitride light emitting diodes

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2008
G. Chen
Abstract The performance of III-nitride based high-power light emitting diodes (LEDs) is reviewed. Direct color high-power LEDs with 1 × 1 mm2 chip size in commercial LUXEON® Rebel packages are shown to exhibit external quantum efficiencies at a drive current of 350 mA ranging from ,60% at a peak wavelength of ,420 nm to ,27% at ,525 nm. The short wavelength blue LED emits ,615 mW at 350 mA and >2 W at 1.5 A. The green LED emits ,110 lm at 350 mA and ,270 lm at 1.5 A. Phosphor-conversion white LEDs (1 × 1 mm2 chip size) are demonstrated that emit ,126 lm of white light when driven at 350 mA and 381 lm when driven at 1.5 A (Correlated Color Temperature, CCT , 4700 K). In a similar LED that employs a double heterostructure (DH) insign instead of a multi-quantum well (MQW) active region, the luminous flux increases to 435 lm (CCT , 5000 K) at 1.5 A drive current. Also discussed are experimental techniques that enable the separation of internal quantum efficiency and extraction efficiency. One technique derives the internal quantum efficiency from temperature and excitation-dependent photoluminescence measurements. A second technique relies on variable-temperature electroluminescence measurements and enables the estimation of the extraction efficiency. Both techniques are shown to yield consistent results and indicate that the internal quantum efficiency of short wavelength blue (, , 420 nm) high-power LEDs is as high as 71% even at a drive current of 350 mA. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Recent progress of high efficiency white LEDs

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2007
Yukio Narukawa
Abstract We fabricated three types of white light emitting diodes (LEDs). The first is the white LED, which has a high general color rendering index (Ra) of 97 and CRI-No. 9 of 96. The CRI-No. 9 denotes the color reproduction in the red region. These values are higher than those of a tri-phosphor fluorescent lamp (Ra = 85 and CRI-No. 9 = 8). The second is the high efficiency white LED fabricated from the small-size high efficiency blue LED chip. The output power (Po), the external quantum efficiency (,ex) and wall-plug efficiency (WPE) of the small-size blue LED were 35.0 mW, 63.3% and 56.3%, respectively, at a forward-bias current of 20 mA. The luminous flux (,), luminous efficiency (,L) and WPE of the second white LED are 8.6 lm, 138 lm/W and 41.7%, respectively. The luminous efficiency is 1.5 times greater than that of a tri-phosphor fluorescent lamp (90 lm/W). The third is the high power white LED fabricated from the larger-size blue LED chip. Po, ,ex and W.P.E. are 458 mW, 47.2% and 39.7%, respectively, at 350 mA. ,, ,L and WPE of the third white LED are 106 lm, 91.7 lm/W and 27.7% at 350 mA, respectively. Moreover, , of 247 lm and 402 lm at 1 A and 2 A are obtained, respectively. , at 2 A is equivalent to the total flux of a 30 W incandescent lamp. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]