Study of An Unsymmetrical Shadow Mask PDP with High Luminous Efficacy

A new shadow mask plasma display panel （SMPDP） is presented in this article. The unsymmetrical geometry structure of the discharge cell is its main feature. A macro-cell with a ratio of 40：1 was designed and fabricated. The geometrical parameters and electrode＇s structure of the discharge cell of the unsymmetrical SMPDP were optimized. Compared with current SMPDP, its luminous efficiency was obviously improved. Then a 32-inch wide video graphics array （WVGA） unsymmetrical SMPDP with a luminous efficacy of 1.8 Lm/W was produced.

Theoretical and experimental analysis of the effects of the series resistance on luminous efficacy in GaN-based light emitting diodes

In this paper, a new equivalent circuit model of GaN-based light emitting diodes （LEDs） is established. The impact of the series resistance to luminous efficacy is simulated using the MATLAB software. GaN-based LEDs with different n- contact electrode materials （LEDs with Ni/Au and LEDs with Cr/Au） are fabricated. By comparing and analyzing the results of performances, we concluded that both the series resistance and the carrier loss could affect the luminous efficacy severely. LEDs with lower series resistance have higher luminous efficacy and its efficiency droop is alleviated simultaneously. To improve luminous efficacy, the fabrication process should be optimized for lower series resistance.

Theoretical Modeling of Luminous Efficacy for High-Power White Light-Emitting Diodes

The photometric characteristics of high-power white light-emitting diode （LED） devices are investigated. A theoretical model for the luminous efficacy o[ high-power white LED devices and LED systems is proposed. With the proposed theoretical model, the mechanism of the luminous efficacy decrease is explained. Meanwhile, the model can be used to estimate the luminous efficacy oF LEDs under general operation conditions, such as different operation temperatures and injection currents. The wide validity of the luminous efficacy model is experimentally verified through the measurements of different types of LEDs. The experimental results demonstrate a high estimation accuracy. The proposed models not only can be applied to estimate the LED photometric performance, but also is helpful for reliability research of LEDs.

Luminous efficacy and color rendering index of high power white LEDs packaged by using red phosphor

We packaged a series of high power white LEDs by covering the blue LED chips with yellow phosphor, red phosphor and the two phosphors mixed by appropriate mass ratio, respectively, and discussed the excitation and emission spectrum of yellow phosphor and red phosphor and the characteristics of the LEDs. We found that the luminous efficacy of the white LEDs covered with the two phosphors mixed by appropriate mass ratio was lower than that of the white LEDs covered with yellow phosphor, but the color rendering index was improved observably.

Correlated Color Temperature Tunable Multi-chip Light Emitting Diodes Light Source Design

One of the methods to derive white light from light emitting diodes(LEDs)is the multi-chip white LED technology,which mixes the light from red,green and blue LEDs.Introduced is an optimal algorithm for the spectrum design of the multi-chip white LEDs in this paper.It optimizes the selection of single color LEDs and drive current controlling,so that the multi-chip white LED achieves the target correlated color temperature(CCT),as well as high luminous efficacy and good color rendering.A CCT tunable LED light source with four high-power LEDs is realized based on the above optimal design.Test results show that it maintains satisfactory color rendering and stable luminous efficacy across the whole CCT tuning range.Finally,discussed are the design improvement and the prospect of the future applications of the CCT tunable LED light source.

Composition and luminescence properties of highly robust green-emitting LuAG:Ce/Al_(2)O_(3)composite phosphor ceramics for high-power solid-state lighting

The major advantage of laser lighting over white light-emitting-diode is the possibility to achieve ultra-high luminance.However,phosphors usually suffer laser-induced luminescence saturation,which limits the peak luminance of laser lighting devices.The aim of the present study is to develop LuAG:Ce/Al_(2)O_(3)composite ceramics(LACCs)with a high saturation threshold for high-luminance laser lighting.Owning to the rigid crystal structure,proper synthetic process,and optimized thermal design,the LACCs possess small thermal quenching(16%loss in luminescence at 225℃),high quantum yield(>95%),and excellent luminescence properties.When the LACCs are irradiated by blue laser diodes in a reflection mode,a high luminous flux of 4634 lm and luminous efficacy of 283 lm·W^(−1)are realized.Furthermore,they show no sign of luminescence saturation even when the power density reaches 20.5 W·mm^(−2).With these favorable properties,the designed LACCs show great potential in high-luminance laser lighting.

Composition and structure design of three-layered composite phosphors for high color rendering chip-on-board light-emitting diode devices

A three-layered phosphor structure was designed and prepared by the spin coating of BaSi_(2)N_(2)O_(2):Eu(cyan-emitting)and(Sr,Ca)AlSiN_(3):Eu(red-emitting)phosphor films on the yellowemitting Y_(3)Al_(5)O_(12):Ce(YAG:Ce)phosphor ceramic synthesized by the solid-state reaction under vacuum sintering.In order to achieve high color rendering lighting,the influence of the composition and structure of the three-layered phosphors on the optical,thermal,and electrical properties of the chip-on-board(COB)packaged white-light-emitting diodes(WLEDs)was studied systematically.The WLED with the structure of“red+cyan+yellow”(R+C+Y)three-layered phosphor generated neutral white light and had a luminous efficacy of 75 lm/W,the fidelity index(R_(f))of 93,the gamut index(R_(g))of 97,and the correlated color temperature(CCT)of 3852 K.Under the excitation of laser diode(LD),the layer-structured phosphor yielded the white light with a luminous efficacy of 120 lm/W,color rendering index(CRI)of 90,and CCT of 5988 K.The result indicates that the three-layered phosphor structure is a promising candidate to achieve high color rendering and high luminous efficacy lighting.

Peak wavelength selection guides of chip and phosphors for phosphor-converted white light-emitting diodes

The dependences of light efficiency of radiation （LER） and color-rendering index （CRI） of trichromatic white light-emitting diode （wLED）, composed of blue LED die, green/yellow, and red phosphors, on the peak wave- length of each primary were investigated by theoretical calculations, at correlative color temperature （CCT） from 2,700 to 6,500 K. The peak wavelength of InGaN based blue LED chip ranges from 450 to 471 nm, while those of Ca3Sc2Si3012：Ce3＋, b-SiA1ON：Eu2＋, and Y3A15012：Ce3＋ based green/yellow phosphors range from 511 to 572 nm, and those of Sr2SisN8：Eu2＋ and CaA1SiN3：Eu2＋ red phosphors range from 620 to 650 nm, which cover almost all the practically used, commercially available wave bands until now. Then, based on the results, selection guides of peak wavelengths for blue LED chip and phosphors to obtain tradeoff LER 〉280 lm.W-1 as well as CRI 〉80 in all CCTs are proposed. The favorable wave bands of each primary are suggested.