Warm Color Temperature Research Articles

Estimating SpO2 with Deep Oxygen Desaturations from Facial Video Under Various Lighting Conditions: A Feasibility Study.

This paper presents a feasibility study to collect data, process signals, and validate accuracy of peripheral oxygen saturation (SpO2) estimation from facial video in various lighting conditions. We collected facial videos using RGB camera, without auto-tuning, from subjects when they were breathing through a mouth tube with their nose clipped. The videos were record under four lighting conditions: warm color temperature and normal brightness, neutral color temperature and normal brightness, cool color temperature and normal brightness, neutral color temperature and dim brightness. The air inhaled by the subjects was manually controlled to gradually induce hypoxemia and lower subjects' SpO2 to as low as 81%. We first extracted the remote photoplethysmogram (rPPG) signals from the videos. We applied the principle of pulse oximetry and extracted the ratio of ratios (RoR) for two color combinations: Red/Blue and Red/Green. Next, we assessed SpO2 estimation accuracy against the ground truth, a Transfer Standard Pulse Oximeter. We have achieved an RMSE of 1.93% and a PCC of 0.97 under the warm color temperature and normal brightness lighting condition using leave-one-subject-out cross validation between two subjects. The results have demonstrated the feasibility to estimate SpO2 remotely and accurately using consumer level RGB camera with suitable camera configuration and lighting condition.Clinical Relevance- This work demonstrates that SpO2 can be estimated accurately using an RGB camera without auto-tuning and under warm color temperature, enabling continuous SpO2 monitoring applications that require noncontact sensing.

Indoor light energy harvesting for battery-powered sensors using small photovoltaic modules.

As interest in Internet-of-Things (IoT) devices like wireless sensors increases, research efforts have focused on finding ways for these sensors to self-harvest energy from the environment in which they are installed. Photovoltaic (PV) cells or mini-modules are an intuitive choice for harvesting indoor ambient light, even under low light conditions, and using it for battery charging and powering of these devices. Characterizations of battery charging, for small rechargeable batteries from low charge to full charge, have been investigated using PV mini-modules of equal area. We present battery charging results using three different PV technologies, monocrystalline silicon (c-Si), gallium-indium-phosphide (GaInP) and gallium-arsenide (GaAs) under a warm color temperature (3000 K) LED lighting at an illuminance of 1000 lx. Battery charging times are shortest for the more efficient GAInP and GaAs mini-modules whose spectral response are a better match to the LED test source, which contains mostly visible photons, and longest for the less efficient Si cells. As a demonstration, a wireless temperature sensor mote was attached to the charging circuit and operated to determine its power consumption in relation to the available charging power. The mote's maximum power draw was less than the charging power from the least efficient c-Si mini-module. Our findings affirm the feasibility of utilizing PV under typical indoor lighting conditions to power IoT devices.

Sr8MSm1-xEux(PO4)7 phosphors derived by different synthesis routes: Solid state, sol-gel and hydrothermal, the comparison of properties

A series of new Sr-based phosphors Sr8M2+Sm1-х(PO4)7:xEu3+, M = Mg2+, Zn2+ with β-Ca3(PO4)2-type structure was synthesized and studied. The Sr8MgEu(PO4)7 was obtained by three types of synthetic routs: high temperature solid-state, hydrothermal and sol-gel methods. The influence of synthesis routes and annealing conditions on luminescent properties was studied and analyzed taking into account the data on average crystallite size and grain size determination. It was shown that the synthesis method has a defining role on the phosphor’s properties. The solid-state route gives the best powders crystallinity and the highest intensity of emission. The samples were characterized by strong emission in visible region at 615 nm originating from 5D0 → 7F2 transition of Eu3+ and 600 nm originating from the 5G5/2 → 4H7/2 transition of Sm3+. Also, it was revealed that Zn-substituted samples exhibit higher intensity than Mg-containing ones due to larger particle size and lower scattering of light and higher light absorption. Photoluminescence decay curves were measured and the dependence of decay times on activator concentrations was revealed. The CIE chromaticity coordinates were close to red standard. The prototypes of LED devices were characterized by strong emission with warm correlated color temperature. The investigated compounds can be used as a potential commercial phosphor for solid-state lighting application.

A high efficient and anti-thermal dual-emission blue-green phosphors for warm white LEDs

A series of broadband blue-green phosphors Rb0.5+yNa1.5−y(Li3SiO4)2:xEu2+ (0 ≤ y ≤ 0.4, 0.01 ≤ x ≤ 0.08) were synthesized by the high-temperature solid-state reaction. The powder X-ray diffraction was employed to explore the crystal structural evolution from RbNa3(Li3SiO4)4 to RbNa(Li3SiO4)2 with the increasing of Rb+. The spectra show the optimized composition was determined as y = 0.4. The luminescence, lifetime decay curves and thermal steadily spectra of Rb0.9Na1.1(Li3SiO4)2:xEu2+ phosphors were investigated in detail. The phosphor of Rb0.9Na1.1(Li3SiO4)2:Eu2+ shows suitable visible spectra (450–550 nm, cover the blue and green regions), excellent thermal quenching (104%@150 °C of the initial integrated intensity at room temperature under 396 nm excitation) and broad excitation spectrum (320–450 nm). Finally, a commercial near-UV LED devices (395 nm) were fabricated with the Rb0.9Na1.1(Li3SiO4)2:Eu2+ phosphor as blue-green and commercial red phosphor CaAlSiN3:Eu2+ with a warm color temperature of 3104 K and a color rendering index of 91.8. This result indicated that Rb0.9Na1.1(Li3SiO4)2:Eu2+ may be a promising blue-green phosphor for indoor lighting.

Correlation Analysis of Image Reproduction and Display Color Temperature Change to Prevent Sleep Disorder

This paper aims to determine the effect of the smartphone warm color temperature function that relieves display's HEVL (high-energy visible light and short wavelength series blue light), which is known to cause suppression of melatonin secretion on actual image reproduction quality. For this study, the author of this paper measured the display based on the color difference in 26 sampling colors. It was found that for correlated color temperature (CCT) of 4000 K or less, the color difference rose sharply, centering around red and green. In hardware or software, a low CCT was realized by reducing the output centered on blue and green, but in actual color quality, a problem arose in the red and green channels. As far as tone gradation is concerned, ΔE increased for CCT of 4500 K or less while the accuracy of the shadow detail was reduced. With regard to color gamut reproduction, for the coverage of sRGB color space, the color gamut became narrow for CCT of 5500 K or less, and for volume, the color gamut became narrow sharply for CCT of 4000 K. It was found that the maximum CCT changes to prevent a decline in melatonin secretion at a level of minimizing the degradation of image quality is 4000-4500 K.

Electrical impedance spectroscopy analyses and optical properties of the bismuth lutetium tungstate BiLuWO6

ABSTRACTBiLuWO6 was synthesized by a solid state reaction at 1000°C. The sample was initially compacted under ambient conditions to form a cylindrical pellet and then characterized by scanning electron microscopy, the electrical properties were determined from Electrical Impedance Spectrometry, under air, in the temperature range of 400 to 700°C. Nyquist representations were interpreted in terms of equivalent circuits, involving intrinsic and extrinsic conduction mechanisms. UV-Vis diffuse reflectance spectra infers the presence of an indirect bandgap, both direct and indirect assumption were carried out to calculate the band gap. The CIE chromaticity diagram were presented on the basis of the photoluminescence under UV, BiLuWO6 exhibits an orange emission and a warm color temperature.

Novel emission-tunable oxyapatites-type phosphors: Synthesis, luminescent properties and the applications in white light emitting diodes with higher color rendering index

Developing color-tunable phosphors via the introduction of co-doping activators and sensitizers to the host with energy transfer processes has been a state-of-the-art topic for a long time. In this work, novel emission-tunable oxyapatites-type Ba10(PO4)6O:Eu2+,Tb3+/Li+ phosphors were prepared via a high temperature solid state reaction for the applications in white light emitting diodes (w-LEDs) with higher color rendering index. Tunable colors from blue to green can be realized in the Ba10(PO4)6O:Eu2+,Tb3+/Li+ by varying the relative ratios of Eu2+ to Tb3+, showing good absorption in the range of 230–400 nm. The energy transfer mechanism from Eu2+ to Tb3+ ions was demonstrated to be a quadrupole-quadrupole interaction by combining the Inokuti-Hirayama (IH) model and Reisfeld's approximation. Importantly, a prototype white lamp was packaged by mixing Ba9.83(PO4)6O: 0.03Eu2+, 0.07Tb3+, 0.07Li+ and commercial red phosphor CaAlSiN3: Eu2+, and the lamp exhibits a higher color rendering index (Ra = 92 and R9 = 56) and warm correlated color temperature of 4361 K for the actual application. Better luminescent properties compared to commercial Y3Al5O12:Ce3+-based w-LEDs, indicating that Ba10(PO4)6O: Eu2+, Tb3+/Li+ phosphors are emerging as potential phosphor-converted w-LEDs.

KLaSr3(PO4)3F (Re=Tb3+/Eu3+/Eu2+): Promising Multi-Color Luminescence Phosphors forn-UV/UV White LEDs

Among inorganic phosphors used in solid-state lighting, the warm white light phosphors have drawn significant attention because of their high color rendering (CRI) and appropriate warm correlated color temperature (CCT). Herein, novel green emission KLa0.90Tb0.10Sr3(PO4)3F and red emission KLa0.90Eu(3+)0.10Sr3(PO4)3F phosphors were successfully synthesized for the first time. Besides, the phase constitution and photoluminescence properties were investigated in detail. The KLa0.90Tb0.10Sr3(PO4)3F phosphor shows a green emission with a maximum at 545 nm under excitation of 231 nm, while KLa0.90Eu(3+)0.10Sr3(PO4)3F displays a red emission centered at 617 nm excited at 393 nm. Temperature-dependent emission spectra reveal that these phosphors have better thermal stability and color stability. What is more, the white light emission phosphor can be generated by mixing three kinds of KLaSr3(PO4)3F:Re phosphors (Re=Eu2+, Tb3+, and Eu3+), exhibiting a CRI of ∼85 and a warm CCT of ∼3946 K. All the results indicated that the white light emission phosphor with high color rendering and appropriate warm correlated color temperature could be reached by combining these tri-color phosphors with proper ratio.

Attraction of Insects to Incandescent, Compact Fluorescent, Halogen, and Led Lamps in a Light Trap: Implications for Light Pollution and Urban Ecologies

ABSTRACT: The widespread use of electric lamps has created “ecological light pollution” and “artificial light ecology.” Given the important role of insects in ecosystems, how they are affected by light pollution deserves attention. Lamps designed for lighting small areas around residences are used in abundance, but studies specifically examining them are scarce. This study used a light trap to capture insects for 60 summer nights in a suburban town in Virginia, USA. During each night of trapping, one of five different light bulbs was used in the trap (incandescent, compact fluorescent, halogen, warm color temperature LED, or cool color temperature LED). The data suggest that fewer insects overall are attracted to bulbs using LED technology than bulbs using incandescent technology. This difference was also observed in the orders Lepidoptera and Diptera. These results support the use of LED bulbs to reduce the insect attraction and mortality caused by the use of artificial lights at night.

Efficient hybrid white light-emitting diodes by organic-inorganic materials at different CCT from 3000K to 9000K.

The hybrid white light-emitting didoes (LED) with polyfluoren (PFO) polymer and quantum dot (QD) was investigated using dispensing method at the different correlated color temperature (CCT) for cool and warm color temperature. This result indicates that the hybrid white LED device has the higher luminous efficiency than the convention one, which could be attributed to the increased utilization rate of the UV light. Furthermore, the CIE 1931 coordinate of high quality white hybrid LED with different CCT range from 3000K to 9000K is demonstrated. Consequently, the angular-dependent CCT and the thermal issue of the hybrid white LED device were also analyzed in this study.

The Effects of Illuminance and Correlated Color Temperature on Visual Comfort of Occupants' Behavior

The preferred illumination environment in accordance with the actions taken by the occupants of the rooms in residences differs significantly between different cultures and circumstances in and out of the country. In this regard, the purpose of this study is to evaluate the visual performance of various illumination environments in residential spaces by allowing the participants of the experiments to select the kind of illumination environment they prefer as the occupants of the room. For this purpose, we prepared a mock-up residential space of <TEX>$6.2m{\times}4.5m{\times}2.5m$</TEX>, where the experiments for this study were conducted. Then, three illuminance settings (30lx, 100lx, and 150lx) and three color temperature settings (2700k, 4000k, and 6500k) were selected as the properties of the physical environment where the tests were to be conducted. The survey was conducted with 30 study subjects, with whom the level of visual comfort and the lighting adjustment evaluation by different activities were carried out. The level of visual comfort in lighting in a residential context turned to be more influenced by the color temperature and illuminance compared to other factors. Except for the test item, 'comfort,' all test items showed positive reactions when the illuminance was 150lx, which was rather light. In 'comfort,' the test subjects appeared to prefer warm color temperature of 2700k. As we allowed the occupants to adjust the lighting environment in accordance with the conditions of the subjects and the activities they performed, the subjects regarded 150lx - 4000k setting as comfortable, while they preferred 150lx-5400k configuration for working. In case of resting, the subject answered that the configuration of 30lx -2700k setting to be visually comfortable.

Effects of Color Temperature and Brightness on Electroencephalogram Alpha Activity in a Polychromatic Light-emitting Diode

ObjectiveIt has been reported that working and learning efficiency might be increased through artificially controlling the color temperature and brightness of light. However, the neurological bases of these outcomes are not well established. Our study was designed to observe whether electroencephalogram (EEG) alpha frequency, as a candidate biological marker, demonstrates significant changes in response to alterations of specific light parameters.MethodsThirty-two healthy subjects performed cognitive tasks under four different polychromatic light conditions: a combination of two different levels of color temperature (2766K vs. 5918K) and brightness (300 lux vs. 600 lux). Spectrum analyses were performed on alpha frequency.ResultsSubjects reported that they felt more pleasant in bright conditions and more relaxed in warm color temperature conditions. Our findings indicate that alpha power increases in warm, low-light and cool, high-light conditions, and there is a significant interaction between color temperature and brightness.ConclusionEEGs might serve as a useful biological marker for further research related to the effects of polychromatic light on cognitive function.

Fabrication of warm, high CRI white LED using non-cadmium quantum dots

We reported on the synthesis of two bright non-cadmium quantum dots (QDs) of green (512 nm)-emitting InP/ZnS and orange (583 nm)-emitting CuInS2 (CIS)/ZnS core/shell and their application for the fabrication of solid-state lighting device. The spectral overlap between absorptions from both QDs and emission from InGaN-based blue light-emitting diode (LED) chip was excellent. Thus, the efficient down-conversion of blue-to-QD emission for the generation of white light was accomplished by sequentially dispensing InP/ZnS QDs on top of CIS/ZnS ones within epoxy resin. The white QD-LED generated a high-quality white light with a high color rendering index of 90 and a warm color temperature of 3803K under a drive current of 20 mA. Drive current-dependent variations of its primary electroluminescent properties were investigated in details.

Warm with high color rendering index white light from hybridization of Ca2BO3Cl:Eu2+ yellow phosphor and CdSe/ZnS nanocrystals

Yellow emitting Ca2BO3Cl:Eu2+ phosphor was prepared by solid state reaction at 900°C. The particle was monoclinic crystal structure, and showed broad band emission at around 540–590nm due to the 5d–4f transition. Single Ca2BO3Cl:Eu2+ phosphor converted white LED exhibited the CIE coordinates of (0.3441, 0.2675) with low CRI of 67.4. Hybridization of Ca2BO3Cl:Eu2+ with 535 and 610nm emitting CdSe/ZnS nanocrystals contributed to increasing white spectrum and generated the warm color temperature (4055K) with high CRI (83.9) of white light. The acceptable color stability was also observed from (0.3687, 0.3051) at 20mA to (0.3645, 0.3101) at 80mA.

New yellow Ba0.93Eu0.07Al2O4 phosphor for warm-white light-emitting diodes through single-emitting-center conversion

Phosphor-converted white light-emitting diodes for indoor illumination need to be warm-white (i.e., correlated color temperature <4000 K) with good color rendition (i.e., color rendering index >80). However, no single-phosphor, single-emitting-center-converted white light-emitting diodes can simultaneously satisfy the color temperature and rendition requirements due to the lack of sufficient red spectral component in the phosphors’ emission spectrum. Here, we report a new yellow Ba0.93Eu0.07Al2O4 phosphor that has a new orthorhombic lattice structure and exhibits a broad yellow photoluminescence band with sufficient red spectral component. Warm-white emissions with correlated color temperature <4000 K and color rendering index >80 were readily achieved when combining the Ba0.93Eu0.07Al2O4 phosphor with a blue light-emitting diode (440–470 nm). This study demonstrates that warm-white light-emitting diodes with high color rendition (i.e., color rendering index >80) can be achieved based on single-phosphor, single-emitting-center conversion. Scientists have developed a yellow phosphor that can be used to provide a pleasing white light with a warm color temperature when combined with a blue light-emitting diode (LED) chip. Although YAG: Ce-based white LEDs show great promise as a highly efficient and long-lasting form of domestic lighting, their cool bluish-white light makes them undesirable for use in the home. Scientists from the USA and China have now shown that a new phosphor, Ba0.93Eu0.07Al2O4, when combined with a blue InGaN LED, provides a pleasing white light with a warm colour temperature of less than 4000K and a high colour-rendering index of more than 80. The phosphor has an orthorhombic structure and was manufactured by carbothermal reduction and vapour phase deposition in a tube furnace system. This work suggests that high-quality, warm-white lighting can be achieved using a combination of a single phosphor with single-emitting-center and a blue LED chip.

Near UV-pumped green-emitting Na3(Y,Sc)Si3O9:Eu2+ phosphor for white-emitting diodes

A series of iso-structural green-emitting Na3(Y,Sc)Si3O9:Eu2+ phosphors with different Y/Sc ratios have been synthesized by a solid-state reaction. All of the phosphors exhibited strong broad absorption bands in the near ultraviolet (n-UV) range, and gave bright green emission upon 365 nm excitation light. As for the composition-optimized Na3Y0.3Sc0.7Si3O9:Eu2+ phosphor, the critical Eu2+ quenching concentration (QC) was determined to be about 3 mol%, and the corresponding QC mechanism was verified to be the dipole–quadrupole interaction. The fluorescence decay curves, temperature dependence photoluminescence and CIE value of Na3Y0.3Sc0.7Si3O9:Eu2+ phosphors were discussed. A white light-emitting diode (LED) lamp was fabricated based on the green-emitting Na3Y0.3Sc0.7Si3O9:Eu2+ phosphor and combining a 370 nm n-UV chip and the commercial blue-emitting BaMgAl10O17:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors. The produced white-light n-UV LED lamp gave CIE chromaticity coordinates of (0.3690, 0.3782), a high color rendering index of 85.6 and a warm color temperature of 2300 K.

Fabrication of high color rendering index white LED using Cd-free wavelength tunable Zn doped CuInS_2 nanocrystals

Highly luminescent Cd-free Zn doped CuInS(2) nanocrystals (ZCIS NCs) were synthesized, and their properties were evaluated using X-ray diffraction, Raman, UV, and photoluminescence. The crystal structure of the ZCIS NCs was similar to the zinc blende, and the lattice constant decreased with increasing Zn concentration. By incorporation of Zn, the emission wavelength was tuned from 536 to 637 nm with concomitant enhancement of the quantum yield up to 45%. A white light emitting diodes, integrating dual ZCIS NCs (λ(em) = 567, and 617 nm) and a 460 nm InGaN LED, exhibited a high color rendering index of 84.1 with a warm color temperature of 4256.2K. The CIE-1931 chromaticity coordinates were slightly shifted from (0.3626, 0.3378) at 20 mA to (0.3480, 0.3206) at 50 mA.

Crystal structure of blue–white–yellow color-tunable Ca4Si2O7F2:Eu2+,Mn2+ phosphor and investigation of color tunability through energy transfer for single-phase white-light near-ultraviolet LEDs

The crystal structure of Ca4Si2O7F2:Eu2+,Mn2+ was refined and determined from X-ray diffraction (XRD) profiles obtained using a synchrotron light source by the Rietveld refinement method. It was found to crystallize into a monoclinic structure with the P21/c(14) space group. On examining the Mn2+-concentration-dependent photoluminescence properties, we found that the emission colors could be tuned from blue (0.152, 0.112) to white-light (0.351, 0.332) and eventually to yellow (0.430, 0.423) through energy transfer by changing the Eu2+/Mn2+ ratio. Moreover, energy transfer from a sensitizer Eu2+ to an activator Mn2+ occurs via a resonance-type dipole–quadrupole interaction mechanism, and the critical distances of the energy transfer were calculated to be 11.66 A and 12.61 A using concentration quenching and spectral overlap methods, respectively. Combining a 400 nm near-ultraviolet (NUV) chip and a single-phase white-emitting (Ca0.96Eu0.01Mn0.03)4Si2O7F2 phosphor produced a white-light NUV LED with CIE chromaticity coordinates of (0.347, 0.338) and a warm color temperature of 4880 K.

Infrared Photometric Study for theIRAS1 Jy Sample of Ultraluminous Infrared Galaxies

The Two Micron All Sky Survey observation of the IRAS 1 Jy sample of ultraluminous infrared galaxies (ULIRGs) is presented in this paper. Together with the IRAS photometric data, the properties and energy sources of the IRAS 1 Jy sample of ULIRGs in the near- and far-infrared are discussed. It is shown that most sources, not only Seyfert galaxies but also H II and LINER galaxies, have a radiation mechanism with a power-law continuum in the near- infrared. All Seyfert 1 sources and some Seyfert 2 sources with hidden broad-line regions (BLRs) have much redder colors and steeper spectral indices in the near- infrared, indicative of an extremely strong energy source from the central active galactic nucleus. Almost all sources have thermal radiation indicative of starburst domination in the IRAS region; in particular, all Seyfert 1 sources and many Seyfert 2 sources with hidden BLRs have lower [25]-[60] colors, indicative of a flatter spectral continuum and a rather warm color temperature in the 25-60 mu m region. However, all kinds of sources have similar [60]-[100] color distributions, indicative of similar energy sources from the enhanced heating in active star-forming regions and very cold material and also indicative of the quite small influence from the central activity in the 60-100 mu m region. In addition, all Seyfert 1 sources and some Seyfert 2 sources with hidden BLRs have much larger absolute magnitudes in the K band compared with other sources. The results presented in this paper may further help us to understand the physical properties of ULIRGs.