Luminous Efficacy Of Radiation Research Articles

Synthesis, luminescence and photometric characteristics of Ca0.5La(MoO4)2:Ln3+ (Ln = Eu, Tb, Dy) phosphors

Ca0.5La(MoO4)2:Ln3+ phosphors, where Ln = 4, 8, 12, 16, and 20 mol% of Eu, Tb, or Dy, were successfully synthesized by a conventional solid-state reaction method at 900 °C for 3 h. The Ca0.5La(MoO4)2:Ln3+ phosphors exhibit a scheelite tetragonal crystal structure belonging to the I41/a space group. The strong absorption bands seen in Fourier transform infrared (FTIR) spectra confirm that F2(ν3) modes of vibration are IR active. The photoluminescence(PL) spectra reveal that, under optical excitation, the as-synthesized phosphors show high intensity narrow emission bands in the red (615 nm), and green (545 nm), and yellow (570 nm) regions for samples doped with Eu3+, Tb3+, and Dy3+ ions, respectively. The critical concentrations of Eu3+, Tb3+, and Dy3+ as dopants in Ca0.5La(MoO4)2 were found to be 16, 12 and 12 mol%, respectively. Thereafter, concentration quenching effect occurred in the solid solutions. The fluorescence decay times for the major transitions of 5D0 → 7F2, 5D4 → 7F5, and 4F9/2 → 6H13/2 were estimated for different doping concentrations of Eu3+, Tb3+, and Dy3+ in Ca0.5La(MoO4)2, respectively. To determine the color purity and emission quality of the phosphor, photometric parameters such as color chromaticity coordinates, color correlated temperature (CCT), color rendering index (CRI), and luminous efficacy of radiation (LER) were estimated using the spectral energy distribution functions of the Ca0.5La(MoO4)2:Ln3+ phosphors.

Tuning the correlated color temperature of white LED with a guest-host liquid crystal.

We demonstrate an electro-optic method to tune the correlated color temperature (CCT) of white light-emitting-diode (WLED) with a color conversion film, consisting of fluorescent dichroic dye doped in a liquid crystal host. By controlling the molecular reorientation of dichroic dyes, the power ratio of the transmitted blue and red lights of the white light can be accurately manipulated, resulting in different CCT. In a proof-of-concept experiment, we showed that the CCT of a yellow phosphor-converted WLED can be tuned from 3200 K to 4100 K. With further optimizations, the tuning range could be enlarged to 2500 K with fairly good color performance: luminous efficacy of radiation (LER) > 300 lm/W, color rendering index (CRI) > 75, and Duv < 0.005. Besides, the operation voltage is lower than 5 V and good angular color uniformity is achieved with remote-phosphor coating. This approach is promising for next generation smart lighting.

Red-blue-green solid state light sources using a narrow line-width green phosphor

We demonstrate that using a narrow line-width green phosphor with the peak wavelength closely aligned with the peak in the human eye sensitivity significantly improves the Luminous Efficacy of Radiation (LER) for Red-Green-Blue (RGB) emitters. Compared to the traditional RGB sources, the improvement in LER of 20 lm/W can be achieved. Combining the narrow band green phosphor with conventional wide band red and blue phosphors allows for trading off these improvements against the deviation from the Planckian locus for even higher LER. The light sources with the narrow line green phosphor are particularly promising for high energy efficiency and high intensity illumination, where somewhat compromises can be made in the color quality such as in automotive, outdoor spaces, industrial ware-houses, public places (train stations, airports) etc..

Toward a Replacement of the CIE Color Rendering Index for White Light Sources

ABSTRACTThe CIE color rendering (fidelity) index (CRI) has remained unchanged for over four decades. Most, if not all, of its components could be updated to more state-of-the-art methods. One of the most critical components of any color rendering (fidelity) metric is the test sample selection. This article therefore addresses the importance of uniform sampling of wavelength space to avoid selective optimization—that is, taking advantage of the unequal contributions of different wavelength regions to the general color rendering score—of light source spectral power distributions. It summarizes the development of a mathematical sample set with undistorted spectral sensitivity, the HL17 set. The set is used in a recently proposed update, the CRI2012 general color rendering index. To assess the impact of the spectrally uniform sample set on color fidelity scores, the CRI2012 index values for each of a set of 139 lamps were compared with those of the CIE CRI. In addition, the impact of updating the other components was investigated. A mean and maximum absolute difference of respectively 5.9 and 21.8 index units were found between the CRI2012 and CIE CRI, although the largest part—respectively 4.03 and 19.7 index units—was shown to be the result of updating the color difference engine and the switch to the CIE 10° observer. The analysis also indicated possible past spectral selective optimization of some warm-white tri-band fluorescent sources for high luminous efficacy of radiation (LER) and (just) sufficient CIE Ra values by taking advantage of the spectral nonuniformity of the CIE reflectance set. Adopting a spectrally uniform sample set in a color rendering metric therefore has important practical implications when designing light source spectra. Finally, possible updates and further improvements of the CRI2012 are briefly mentioned.

Phosphor-converted LEDs with low circadian action for outdoor lighting

Dichromatic phosphor-converted (pc) light-emitting diodes (LEDs) with low circadian action are proposed for low-luminance photobiologically safe outdoor illumination. The LEDs feature the partial conversion of blue radiation in an orange phosphor with the resulting correlated color temperature in the "firelight" range of 1700-2500 K. The circadian action factor, which is the ratio of the biological efficacy of radiation due to the excitation of intrinsically photosensitive retinal ganglion cells to the mesopic luminous efficacy of radiation, is considerably lower than that of commercial white pc LEDs. The equivalent general color-rendering index estimated with regard to the reduced color-discrimination ability of human vision at low luminances has appropriate values in between those of common white pc LEDs and high-pressure sodium lamp.

Two-Part Gauss Simulation of Phosphor-Coated LED

Gauss simulation is an effective tool for designing light-emitting-diode (LED) light sources. This paper proposes a new two-part Gauss simulation model to simulate a YAG:Ce phosphor-coated LED (PC-LED). This model divides the emission spectra of YAG:Ce phosphor into two parts, and they use different half spectral widths in the Gauss function to accurately simulate the spectra of YAG:Ce PC-LED. The simulated spectra are similar to the measured spectra of packaged LEDs; most correlated color temperature (CCT) error is less than 4%, color rendering index (CRI) error is less than 2, and luminous efficacy of radiation (LER) error is less than 3% for simulation results. This is a vast improvement on an ordinary single Gauss simulation model. Using the model to analyze the combination of common blue LED and YAG:Ce phosphor helps the design of new white LEDs.

Wavelength dependence of colorimetric properties of lighting sources based on multi-color LEDs

Taking color quality scale (CQS) as color rendering assessment criterion, the parameters including each color LED's peak wavelength λi and fractional radiant flux Ii are optimized using genetic algorithm to maximize the luminous efficacy of radiation (LER) of the spectral power distributions (SPDs) of multi-color white light source with 3 to 7 components while maintaining the deviation of its color and color-rendering capability from that of the reference light source within the specified scope. Then the wavelength dependence of these SPDs is analyzed. It is shown that to achieve a Q(a) greater than 95 (5-color LEDs) or even close to 100 (7-color LEDs), the spectral energy could be concentrated in the range of 410~675 nm, indicating that this wavelength range makes a major contribution to high color rendering properties. Spectra filtering experiments show that spectrum around 580nm is harmful to color rendering. To obtain a white light source composed of 3-color LEDs with CQS Q(a) ≥ 80 and correlated color temperature (CCT) within 2700-6500K, the energy ratios among 410-495nm, 495-595nm, and 595-675nm intervals, can be simplified as that of the reference source with the same CCT.

Luminescence and photometric characterization of K+ compensated CaMoO4:Dy3+ nanophosphors

A series of CaMoO4 phosphors doped with trivalent dysprosium (Dy(3+)) and codoped with potassium (K(+)) ions were prepared by hydrothermal method. The nanostructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD). The results reveal that the obtained powder phosphors are single-phase scheelite structure with tetragonal symmetry and the crystallite size is in the range of 10-60 nm. The emission spectra show a bright yellow emission at 576 nm and blue emission at 487 nm. As a charge compensator, K(+) ions were incorporated into CaMoO4:Dy(3+) phosphors, which enhance the PL intensities depending on the doping concentration of K(+). The CIE parameters such as colour coordinates, colour correlated temperature and luminous efficacy of radiation were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicates the suitability of K(+) compensated CaMoO4:Dy(3+) phosphor for white LED applications.

Spectral optimization of the color temperature tunable white light-emitting diode (LED) cluster consisting of direct-emission blue and red LEDs and a diphosphor conversion LED

The correlated color temperature (CCT) tunable white-light LED cluster, which consists of direct-emission blue and red LEDs as well as phosphor-conversion (PC) LEDs packaged by combining green and orange phosphors with a blue LED die, has been obtained by nonlinear program for maximizing luminous efficacy (LE) of radiation (LER) under conditions of both color rendering index (CRI) and special CRI of R9 for strong red above 90 at CCTs of 2700 K to 6500 K. The optimal peak wavelengths of blue LED, red LED, blue LED die, green and orange phosphors are 465 nm, 628 nm, 452 nm, 530 nm and 586 nm, respectively. The real CCT tunable PC/red/blue LED cluster with CRIs of 90~96, R9s of 90~96, CQSs of 89~94, LERs of 303~358 lm/W, and LEs of 105~119 lm/W has been realized at CCTs of 2722 K to 6464 K. The deviation of the peak wavelength should be less than ± 5 nm for blue LED die, ± 1 nm for red LED, and ± 2 nm for blue LED to achieve the PC/R/B LED cluster with high optical performance.

Optimal spectra of white light-emitting diodes using quantum dot nanophosphors

The relationship and trade-offs between the performance parameters including color rendering index (CRI), luminous efficacy of radiation (LER) and correlated color temperature (CCT) of white LEDs using quantum dot nanophosphors (QD-WLEDs) are investigated for CRI ≥ 80 and LER ≥ 300 lm/W at 1500 K ≤ CCT ≤ 6500 K. The optimal spectra of QD-WLEDs with CCTs of 2700-6500 K have been obtained with a nonlinear program for maximizing LER under conditions of both CRI and a special CRI of R9 strong red above 90 or 95. Furthermore, high performance QD-WLEDs with LER = 381 lm/W for CRI = R9 = 90 and LER = 371 lm/W for CRI = R9 = 95 at CCT = 3000 K, with LER = 361 lm/W for CRI = R9 = 90 and LER = 352 lm/W for CRI = R9 = 95 at CCT = 4500 K, and with LER = 346 lm/W for CRI = R9 = 90 and LER = 338 lm/W for CRI = R9 = 95 at CCT = 5700 K could be achieved. The LERs of high performance white LEDs using QD nanophosphors increase by 13% to 32% compared with that of white LEDs using traditional phosphors.

Colorimetry and efficiency of white LEDs: Spectral width dependence

AbstractThe potential colour rendering capability and efficiency of white LEDs constructed by a combination of individual red, green and blue (RGB) LEDs are analysed. The conventional measurement of colour rendering quality, the colour rendering index (CRI), is used as well as a recently proposed colour quality scale (CQS), designed to overcome some of the limitations of CRI when narrow‐band emitters are being studied. The colour rendering performance is maximised by variation of the peak emission wavelength and relative intensity of the component LEDs, with the constraint that the spectral widths follow those measured in actual devices. The highest CRI achieved is 89.5, corresponding to a CQS value of 79, colour temperature of 3800 K and a luminous efficacy of radiation (LER) of 365 lm/W. By allowing the spectral width of the green LED to vary the CRI can be raised to 90.9, giving values of 82.5 and 370 lm/W for the CQS and LER, respectively. The significance of these values are discussed in terms of optimising the possible performance of RGB LEDs.

Optimization of colour quality of LED lighting with reference to memory colours

Simulated and real tri- and tetrachromatic light-emitting-diode (LED) clusters were optimized for luminous efficacy of radiation (LER) and the memory colour quality metric developed by the authors. The simulated clusters showed no significant differences in achievable colour quality and LER between the different cluster types investigated. The real clusters (composed of commercially available LEDs) showed substantial differences in achievable colour quality and LER between the different cluster types investigated. The real clusters also exhibited a large drop in LER and memory colour quality compared to the simulated clusters due to the limited range of available peak wavelengths and spectral halfwidths. A real tetrachromatic LED lamp, constructed with commercial red, green, blue and warm white LEDs, was optimized for LER and colour quality. In a psychophysical experiment, several aspects of the colour quality of the LED lamp (optimized for 2700 K) and an incandescent lamp were assessed by 18 observers. The visual appreciation (in terms of attractiveness, preference, and memory colour similarity) of the LED lamp was rated significantly higher than the incandescent lamp.

Optimal spectra of the phosphor-coated white LEDs with excellent color rendering property and high luminous efficacy of radiation

A model for spectra of the phosphor-coated white LED (p-W LED) with a blue chip, a red chip, and green and yellow phosphors is presented. The optimal spectra of p-W LEDs with correlated color temperatures (CCTs) of 2700-6500 K have been obtained with a nonlinear program for maximizing luminous efficacy of radiation (LER) under conditions of both color-rendering indices (CRIs) and special CRIs of R9 strong red above 98. The simulation results show that p-W LEDs with one InGaN blue (450 nm) chip, one AlGaInP red (634 nm) chip, and green (507 nm) and yellow (580 nm) silicate phosphors can realize white lights with CRIs of about 98 and special CRIs of R9 for strong red above 98. The average of the special CRIs R9 to R12 for the four saturated colors (red, yellow, green, and blue) is above 95. R13 for the skin of women's faces at about 100, as well as LERs above 296 lm/W at CCTs of 2700-6500 K. LERs of excellent CRI p-W LEDs with one InGaN blue chip, one AlGaInP red chip, and green and yellow silicate phosphors increased by 19-49% when compared with that of excellent CRI p-W LEDs with one InGaN blue chip and green and yellow silicate phosphors, as well as red nitride phosphor.

68.4: Optimal Additive Mixing Approach via Multi‐Color LEDs Platform

AbstractOn the basis of additive mixing approach via multi‐color LEDs, we demonstrated a universal platform to synthesize the spectral power distribution in accordance with possibly highest color rendering performance and luminous efficacy of radiation under a designated correlated color temperature. The platform associated with the optimization algorithm and LED matrix setup allows the use of a feedback mechanism to validate the feasibility of the proposed scheme for the general lighting applications.

Spectral Identification of Lighting Type and Character

We investigated the optimal spectral bands for the identification of lighting types and the estimation of four major indices used to measure the efficiency or character of lighting. To accomplish these objectives we collected high-resolution emission spectra (350 to 2,500 nm) for forty-three different lamps, encompassing nine of the major types of lamps used worldwide. The narrow band emission spectra were used to simulate radiances in eight spectral bands including the human eye photoreceptor bands (photopic, scotopic, and “meltopic”) plus five spectral bands in the visible and near-infrared modeled on bands flown on the Landsat Thematic Mapper (TM). The high-resolution continuous spectra are superior to the broad band combinations for the identification of lighting type and are the standard for calculation of Luminous Efficacy of Radiation (LER), Correlated Color Temperature (CCT) and Color Rendering Index (CRI). Given the high cost that would be associated with building and flying a hyperspectral sensor with detection limits low enough to observe nighttime lights we conclude that it would be more feasible to fly an instrument with a limited number of broad spectral bands in the visible to near infrared. The best set of broad spectral bands among those tested is blue, green, red and NIR bands modeled on the band set flown on the Landsat Thematic Mapper. This set provides low errors on the identification of lighting types and reasonable estimates of LER and CCT when compared to the other broad band set tested. None of the broad band sets tested could make reasonable estimates of Luminous Efficacy (LE) or CRI. The photopic band proved useful for the estimation of LER. However, the three photoreceptor bands performed poorly in the identification of lighting types when compared to the bands modeled on the Landsat Thematic Mapper. Our conclusion is that it is feasible to identify lighting type and make reasonable estimates of LER and CCT using four or more spectral bands with minimal spectral overlap spanning the 0.4 to 1.0 um region.

Solid-state lamps with optimized color saturation ability

Spectral power distribution of trichromatic clusters of light-emitting diodes (LEDs) was optimized for rendering the highest number of colors with a perceptually noticeable gain in chroma (color saturation) out of 1269 Munsell samples. The basic tradeoffs of the number of colors rendered with increased saturation with the number of colors rendered with high fidelity and with luminous efficacy of radiation were established. High-saturation RGB clusters composed of commercially available AlGaInP and InGaN LEDs were modeled for a standard set of correlated color temperatures and the stability of the color saturation ability of the clusters against the drift of peak wavelengths was investigated.

백색 LED와 RGB 멀티칩 LED 조명장치의 특성 분석

LED조명장치는 자동차분야, 항공, 디스플레이, 전송장치 그리고 특수조명등의 응용장치로의 활용이 증가하고 있다. 일반적으로 고출력 RGB 멀티칩 LED는 표시용이나 경관조명용 또는 감성조명용으로 적용되고 백색 LED는 표시용 조명에서 최근 들어 일반조명용으로 적용되고 있으며, 고출력 백색 LED의 출시와 광효율의 증가는 이를 더욱 가속화하고 있다.BR 본 논문에서는 백색 LED와 RGB 멀티칩 LED 조명장치를 동일한 사양으로 제작하여 물리적, 전기적, 광학적 조명특성을 분석하여 향후 LED조명시스템의 제작에 정량적 데이터를 제공하고자 한다. 이를 위해 LED의 주요한 물리적 특성인 방열특성에 대한 성능분석, 전기적 특성의 분석을 위한 전력 및 드라이브 효율에 대한 성능분석을 수행하였고 조명특성을 위한 연색성, 배광특성, 광효율을 측정하였다. 백색 LED와 RGB 멀티칩 LED 조명장치를 활용한 응용장치의 적용방법을 확립하고 나아가 다양한 조명시스템에 LED 조명장치를 적용하는데 참고가 되는 기초 데이터를 제시하고자 한다.

Spectral design considerations for white LED color rendering

White LED spectra for general lighting should be designed for high luminous efficacy as well as good color rendering. Multichip and phosphor-type white LED models were analyzed by simulation of their color characteristics and luminous efficacy of radiation, compared with those of conventional light sources for general lighting. Color rendering characteristics were evaluated based on the CIE Color Rendering Index CRI, examining not only Ra but also the special color rendering indices Ri, as well as on the CIELAB color difference Eab for the 14 color samples defined in CIE 13.3. Several models of three-chip and four-chip white LEDs as well as phosphor-type LEDs are optimized for various parameters, and some guidance is given for designing these white LEDs. The simulation analysis also demonstrated several problems with the current CRI, and the need for improvements is discussed. © 2005

Theoretical Evaluation of Spectral Power Distributions of Radiant Energy from Microcavities.

Characteristics of radiation from microcavities are investigated to verify the luminous efficacy of microcavity radiator that was estimated by John F. Waymouth in 1989. Electromagnetic waves in a rectangular microcavity and a cylindrical microcavity were analyzed based on the waveguide theory. The modes of electromagnetic waves in the microcavities are analyzed using a normalized eigenfunction. The conductivity and permittivity of metals are obtained by analyzing the motion equation of the free electron in the metals. The skin depth of tungsten is estimated with the emissivity of tungsten based on electromagnetic theory. Accordingly it is estimated that the luminous efficacy of radiation from the microcavity is expected to reach 118 lm/W.