High Correlated Color Temperature Research Articles

High correlated color temperature artificial lighting impairs retinal pigment epithelium integrity and chloride ion transport: A potential mechanism for choroidal thinning

Among the environmental factors contributing to myopia, the role of correlated color temperature (CCT) of ambient light emerges as a key element warranting in-depth investigation. The choroid, a highly vascularized and dynamic structure, often undergoes thinning during the progression of myopia, though the precise mechanism remains elusive. The retinal pigment epithelium (RPE), the outermost layer of the retina, plays a pivotal role in regulating the transport of ion and fluid between the subretinal space and the choroid. A hypothesis suggests that variations in choroidal thickness (ChT) may be modulated by transepithelial fluid movement across the RPE. Our experimental results demonstrate that high CCT illumination significantly compromised the integrity of tight junctions in the RPE and disrupted chloride ion transport. This functional impairment of the RPE may lead to a reduction in fluid transfer across the RPE, consequently resulting in choroidal thinning and potentially accelerating axial elongation. Our findings provide support for the crucial role of the RPE in regulating ChT. Furthermore, we emphasize the potential hazards posed by high CCT artificial illumination on the RPE, the choroid, and refractive development, underscoring the importance of developing eye-friendly artificial light sources to aid in the prevention and control of myopia.

Enhanced Visual Performance for In–Vehicle Reading Task Evaluated by Preferences, Emotions and Sustained Attention

The proliferation of electric and hybrid vehicles has made it possible for people to read and work in a stationary vehicle for extended periods. However, the current commonly used in–vehicle lighting design is still centered around driving and driving safety. Following recommendations from the literature, a neutral white color band (4000 K–5000 K) with 50–100 lx at the vehicle table area is favored. Whether this lighting environment can meet the needs to enhance the reading performance in a modern vehicle was investigated in this presented study. Therefore, in total, 12 lighting settings were designed based on combinations of four illuminance levels (50 lx, 100 lx, 150 lx and 200 lx) and three correlated color temperatures (3000 K, 4000 K and 5000 K); we recruited 19 subjects (12 females, 7 males) and let study participants evaluate each condition based on electronic and paper reading. Next, subjective preferences, positive and negative emotions, feeling of fatigue and sustained attention were tested. We found that higher illuminance and higher CCT (Correlated Color Temperature) can significantly improve the performance of in–vehicle readers in most aspects following Kruithof’s law (p < 0.05). Among them, we recommend the combination of 150 lx and 4000 K as the light parameters for in–vehicle reading as a new development guideline. In addition, we also discovered the inconsistency of people’s lighting preferences between in–vehicle spaces and conventional spaces. For indoor lighting, illuminance values up to 1000 lx are still favored. For an in–vehicle function, starting with 200 lx, the preference level and reading performance already declined. In comparison between electronic and paper reading, both were similarly evaluated. These results show that a neutral white light color should be chosen with a horizontal illuminance of maximal 150 lx for a reading light function independent of the reading device. Interdisciplinarily speaking, our findings can be applied in similar small spaces or transportation modes with gentle acceleration and deceleration such as small space hotel rooms, trains, airplanes or ships.

High quantum efficiency and excellent thermal stability in Eu3+ -activated CaY2ZrGaAl3O12 phosphors for wLEDs

There is a high demand for phosphorescent white light-emitting diodes (wLEDs) that possess low correlated color temperature (CCT) and high color rendering index (CRI), as they are considered to be environmentally friendly sources of solid-state illumination. A novel, UV-excited red light emitting Eu3+-activated CaY2ZrGaAl3O12 phosphor was synthesized for the preparation of warm wLEDs with high CRI and low CCT were obtained. Eu3+-doped CaY2ZrGaAl3O12 phosphors were synthesized with varying concentrations of Eu3+ dopant. The luminescence of Eu3+ was thoroughly examined at its optimal concentration of 20 mol%. Surprisingly, CaY2ZrGaAl3O12: 20%Eu3+ exhibits a broad excitation band of 200–550 nm and some sharp excitation peaks, the highest peak is observed at 251 nm. A dazzling red light, ranging from 550 to 750 nm, is emitted by CaY2ZrGaAl3O12: 20%Eu3+ phosphor. The excitation of ultraviolet light at a wavelength of 251 nm was employed, with an impressive internal quantum efficiency of 90.7% and a remarkable thermal quenching resistance. The wLED was packaged with green phosphor (BaMgAl10O17: Eu2+), red phosphor (CaY2ZrGaAl3O12: Eu3+), blue phosphor ((Ba, Sr)2SiO4: Eu2+) and 395 nm NUV LED chip, which emitted a dazzling warm white light when driven at a current of 20 mA. It has excellent CIE color coordinates (0.3893,0.3736), a low correlation color temperature (CCT) of 3738K, and an excellent color rendering index (Ra = 82.1). The application of the prepared new CaY2ZrGaAl3O12: Eu3+ red phosphor in wLED will promote the development of highly efficient luminous materials for healthy solid-state lighting.

Rapid room temperature synthesis of Mn-doped perovskite quantum dots for white-light-emitting diodes

All-inorganic perovskite quantum dots (PQDs) have excellent photoelectric performance, such as high photoluminescence quantum yield (PLQY), narrow full width at half-maximum (FWHM), and emission spectra covering the visible light wavelength. The emission color can be tuned over the full visible spectral region making them promising for white-light-emitting diodes (WLEDs). Further control over the optical and magnetic properties of PQDs can be achieved through doping of transition metal ions such as Mn2+ ions. In this paper, a rapid doping method is employed at room temperature by using strong-acid cation-exchange resin during the metal ions doping process, which shortens the doping time, and Mn:CsPb(Cl/Br)3 QDs were obtained. By controlling the reaction time between strong-acid cation-exchange resin and PQDs, we achieve different levels of manganese doping, resulting in a new, to the best of our knowledge, fluorescence peak at 600 nm. The introduction of strong-acid cation-exchange resin preserves the integrity of the PQD structure, while completing the doping within 30 min. Due to the low cost and mild reaction conditions of resin, it is expected that the Mn:CsPb(Cl/Br)3 QDs can be mass-produced in large quantities. In addition, in order to provide high-quality white light emission, and prevent anion exchange reactions when mixed with CsPbBr3 QDs, the CsPbBr3 QDs are coated with silicon. Finally, by combining ultraviolet-light-emitting diodes (UVLEDs) with the aforementioned PQD mixture, this paper successfully fabricates WLEDs and demonstrates its excellent photoelectric performance. The constructed WLEDs produce warm white light with a high color rendering index (CRI) of 91 and a high correlated color temperature (CCT) of 5966 K, and the luminous efficacy (LE) of WLEDs is 41lmW−1.

Unveiling the luminescence property of Pr-incorporated barium cerate perovskites for white LED applications

Abstract The various structural and conductive attributes of barium cerate, BaCeO3 position it as a highly promising matrix for energy storage purposes. The current study illustrates that barium cerate can be effectively tailored by introducing trivalent praseodymium ions, thereby enhancing its optical properties as well. In this work, single-phased orthorhombic crystalline powders of barium cerate incorporated with Pr3+ (BaCeO3: Pr3+) were synthesized using the gel combustion procedure, followed by calcination. We conducted a comprehensive investigation into their crystal structure, vibrational characteristics, optical properties, and potential applications in wLEDs. The structure refinement indicates that Pr3+ occupies Ce4+ site, which results in the expansion of the cell and facilitates the generation of defects such as Pr Ce ′ ${\mathrm{Pr}}_{\text{Ce}}^{\prime }$ and oxygen vacancies V O ⋅ ⋅ ${V}_{\text{O}}^{\cdot \cdot }$ . By correlating information gathered from diffuse reflectance spectra with that obtained from photoluminescence spectra, we gained a deeper understanding of the electronic level structure and the mechanism of energy transfer. We successfully achieved a finely tuned cool white light emission with very low color purity (CP), a high color rendering index (CRI), and a high correlated color temperature (CCT) with a quantum efficiency of 36.3 % by exciting the material with a 321 nm wavelength. Because of the transfer of energy within activators through dipole–dipole interaction, luminescence quenching occurs when Pr3+ concentration reaches 1 wt%. To the best of our knowledge, this is the initial investigation of luminescence properties of Pr-incorporated barium cerate perovskites.

The dual-model up/down-conversion green luminescence of NaSrGd(MoO4)3: Er3+ and its application for temperature sensing.

Er3+-doped phosphors are widely used as dual-functional optical thermometers due to their distinctive up/down-conversion luminescence and the thermally coupled energy states (2H11/2 and 4S3/2) of Er3+. The development of high-performance Er3+-activated optical thermometers is both an intriguing subject and a formidable challenge in the field. This article investigates the up/down-conversion (UC and DC) photoluminescence properties of NaSrGd(MoO4)3 (NSGM): Er3+. When excited at 375 and 975 nm, the phosphors emit peaks at 530, 550, and 657 nm, corresponding to the 2H11/2, 4S3/2, and 4F9/2 → 4I15/2 transitions of Er3+, with the 4S3/2 → 4I15/2 transition displaying the highest intensity. The optical properties are comprehensively studied through UV-visible absorption, PL spectroscopy, and PLE spectroscopy. Optimal luminescence intensity is achieved at an Er3+ concentration of 4% mol. The resulting chromatic coordinates (x, y) and high correlated color temperature (CCT) values of the doped phosphors yield thermally stable cold emissions in the green region, boasting color purities of approximately 98.76% and 80.74% for DC and UC conversion, respectively. The optical temperature sensing properties of thermally coupled energetic states are explored based on the fluorescence intensity ratio principle. NSGM: 0.04Er3+, under 375 nm light excitation, demonstrates the maximum relative sensitivity of 0.87%/K-1 at 298.15 K, spanning a wide temperature range from 298.15 to 488.15 K. Conversely, under 975 nm light excitation, NSGM: 0.04Er3+ exhibits the maximum relative sensitivity of 0.63%/K-1 over the same temperature range, with temperature uncertainty (δT) less than 0.50 K and repeatability (R) (more than 98%). These findings position this material as a promising candidate for optical thermometer applications. The optical heating capacity of the synthesised phosphor is also determined using optical thermometry results, and heat generation up to approximately 457 K is found, indicating that NSGM: 0.04Er3+ could be useful for photo-thermal therapy.

Synthesis and luminescence properties of a bluish-green -emitting Sr3LiSbO6: Pr3+ phosphor for optoelectronic applications

The present work explores the significance of charge transfer band (CTB) excitation, with large absorption capacity, of Pr3+ doped Sr3LiSbO6 phosphor materials for bluish-green emission. Phosphor materials were synthesized via the conventional high-temperature solid-state method. The formation of phase structure was confirmed by XRD. The structural parameter was estimated from Rietveld refinement. Field emission scanning electron microscopy (FESEM) and High-resolution transmission electron microscopy (HRTEM) coupled with mapping and EDX spectroscopy were employed to get high-resolution images of morphologic structure. Raman and FTIR spectra were investigated to detect the presence of different vibrational levels and functional groups respectively. The elemental compositions were further confirmed via XPS survey scan spectrum and their oxidation state was also explored. The optical band-gap was found to increase first with doping concentration and then start to decrease after doping of 2 mol%, this result was further supported by photoluminescence (PL) emission spectra. PL emission spectra presented the characteristic peaks of Pr3+ due to f-f transitions. PL emission spectra illustrated that the concentration quenching took place at 2 mol% doping of Pr3+, which was governed by dipole-dipole coupling. The decay curves of each sample were recorded for specific excitation and emission wavelengths of 262 nm and 490 nm respectively. All the decay curves were well-fitted with single exponential function. The observed average decay time was 10.5 μs. Afterward, photometric studies including Chromaticity International d’Eclairage (CIE), correlated color temperature (CCT) and color purity (CP) were performed. Calculated CIE values were found to lie in bluish-green regions with lower CP and higher CCT. These results obtained from various characterizations conclude that the proposed Sr3LiSbO6 phosphor, doped with various concentrations of Pr3+ (0 mol% to 7 mol% of Pr3+), reveal their applicability in the field of solid-state lighting for white light emitting diodes.

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting.

The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4̅21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.

Temperature-dependent photoluminescent behavior of millimeter-scale Cs4PbBr6/CsPbBr3 bulk crystals and their application to white light-emitting diodes

The zero-dimensional perovskite composite Cs4PbBr6/CsPbBr3 has attracted significant attention for its remarkable photoluminescence (PL), which remains highly effective even in solid state. This work presents a detailed analysis of the steady-state and time-resolved PL (TRPL) behavior of millimeter-scale Cs4PbBr6/CsPbBr3 crystals over a temperature range of 80 to 360 K, which covers exciton binding energy, phonon energy, and PL peak energy shifting with increasing temperature. According to the results, Cs4PbBr6/CsPbBr3 exhibits high exciton binding energy and phonon energy, with calculated values of 358.7 and 94.8 meV, respectively. Specifically, when the temperature is below ∼235 K, thermal expansion dominates to influence the TRPL and peak energy, whereas electron-phonon interaction becomes the dominant factor as temperature rises from 235 to 325 K. It is found that Cs4PbBr6/CsPbBr3 has a PL behavior similar to CsPbBr3, and characterization and TRPL results demonstrate that nanometer-scale CsPbBr3 crystals embed in the Cs4PbBr6 bulk matrix. Meanwhile, a white light-emitting diode (WLED) device based on Cs4PbBr6/CsPbBr3 with luminous efficiency of 64.56 lm/W is fabricated, and its color coordinate is measured as (0.34, 0.31) under 20 mA, which is in close proximity to the standard white color coordinate. Moreover, the color gamut of the device is measured as 128.66% of the National Television Systems Committee (NTSC). The WLED electroluminescence (EL) spectra show high Correlated Color Temperature (CCT) stability for the working current varying from 5 to 100 mA, and after continuous operation for 12 h, the EL intensity decreases and stabilizes at ∼70% of the initial EL intensity. These findings suggest that Cs4PbBr6/CsPbBr3 crystals are a promising candidate for WLEDs.

Cost effective red emitting Eu3+ doped natural sodium feldspar (NaAlSi3O8) powder and photophysical changes on transition to glassy state

There is a need for low cost red emitting materials for commercial phosphor converted white light emitting diodes (pc-WLEDs) due to low color rendering index (CRI) and high correlated color temperature (CCT) of currently existing InGaN pumped YAG:Ce3+ white LED. The present study involves the synthesis, characterisation and photoluminescence studies of Eu doped albite (NaAlSi3O8: x%Eu3+, x = 0, 0.5, 1, 2, 5). Successful doping of Eu3+ at Na+ site was observed to result in a small expansion of the unit cell. Under 395 nm excitation the phosphors show intense red band at 614 nm due to the trivalent europium ions. There is an enhancement in their red emission as well as internal quantum efficiency from 67 to 73 % with increase in the europium concentration. The luminescence decay lifetime of NaAlSi3O8: x%Eu3+ phosphor is having biexponential decay with short life time in microseconds and long lifetime in milliseconds endowed by their different proximity to sodium vacancies. The powdered sample was also converted to its glassy form by heating at 1200 °C to compare their photophysical properties. High asymmetry ratio and improved PL emission intensity of europium ion was found in the albite glass compared to crystalline powder whereas luminescence lifetime reduces. The CIE chromaticity diagram indicates the high color purity of the synthesized material. The present work demonstrated that the synthesized Eu3+ doped Albite powder and glass as a potential low-cost red emitting phosphor for the UV excitation.

An Ultra‐Broadband Yellow‐Emitting Phosphor KRbCa0.8Mg0.2PO4F:Eu2+ for White Light‐Emitting Diodes with High Color Rendering Index

AbstractPhosphor‐converted white light‐emitting diodes (pc–WLEDs) realized by combining near‐ultraviolet (NUV) chips and multi‐color phosphors are found to be an effective solution to make up the shortcomings of the poor color rendering index and high correlated color temperature of the combination of blue InGaN chips with YAG:Ce3+ yellow phosphor. However, the NUV excited phosphors suffer from deficiencies such as reabsorption and dissonance deterioration rates. To surmount the drawback above, the ion substitution engineering was carried out to the (Rb,K)2CaPO4F:Eu2+ phosphors, and an NUV excited ultra‐broadband yellow‐emitting phosphor was obtained in this work. With the substitution of Mg2+ for Ca2+, the emission intensities of (Rb,K)2CaPO4F:Eu2+ phosphors are significantly improved as well as the thermal stability. Under the excitation of 380 nm, the yellow phosphor KRbCa0.78Mg0.2PO4F:0.02Eu2+ exhibits an ultra‐broad emission band covering the range from 450 to 800 nm with an amazing FWHM of 181 nm. White light with a super‐high color rendering index (Ra = 92.3), appropriate correlated color temperature (5644 K), as well as stable CIE chromaticity coordinates are achieved by the white light‐emitting diodes device fabricated with this yellow phosphor. These excellent performances indicate that KRbCa0.78Mg0.2PO4F:0.02Eu2+ has great potential to be applicated in the NUV excited white LEDs.

Synthesis of Pb‐free Double‐Perovskite Heterojunction (Cs2SnCl6‐Bi3+&Te4+/Cs2GeF6‐Mn4+) with White Emission for LED Application

AbstractLead‐free halide double perovskites have been extensively studied for their application in the display and lighting fields. Owing to their characteristic single white luminescence, double perovskites have led to several developments in the field of white light illumination. However, most of these materials possess poor ambient stability or produce white emissions with high correlated color temperature (CCT) and low color rendering index (Ra), which hinder their application to home and commercial lighting displays. To address these challenges, a Pb‐free double perovskite heterojunction phosphor for white light is designed, namely Cs2SnCl6‐2%Bi3+&4%Te4+/Cs2GeF6‐0.11%Mn4+, which has a low CCT of 3525 K, a high Ra of 90.5, good optical moisture and thermal stability. The pattern and mechanism of epitaxial growth are derived from structural and surface tests. Analyzing the optical properties clarifies the existence of energy transfer modes in this heterojunction material, i.e., from Bi3+ to Te4+, from Bi3+ to Mn4+, and from Te4+ to Mn4+. These results indicate the application prospects of these heterojunction phosphors in the field of white light illumination.

Proper use of light environments for mitigating the effects of COVID-19 and other prospective public health emergency lockdowns on sleep quality and fatigue in adolescents

Coronavirus disease 2019 (COVID-19) remains a public health emergency of international concern, and some countries still implement strict regional lockdowns. Further, the upcoming 2023 Asian Games and World University Games will implement a closed-loop management system. Quarantine can harm mental and physical health, to which adolescents are more vulnerable compared with adults. Previous studies indicated that light can affect our psychology and physiology, and adolescents were exposed to the artificial light environment in the evening during the lockdown. Thus, this study aimed to establish and assess appropriate residential light environments to mitigate the effects of lockdowns on sleep quality and fatigue in adolescents. The participants were 66 adolescents (12.15 ± 2.45 years of age) in a closed-loop management environment, who participated in a 28-day (7-day baseline, 21-day light intervention) randomized controlled trial of a light-emitting diode (LED) light intervention. The adolescents were exposed to different correlated color temperature (CCT) LED light environments (2000 K or 8000 K) for 1 h each evening. The results for self-reported daily sleep quality indicated that the low CCT LED light environment significantly improved sleep quality (p < 0.05), and the blood test results for serum urea and hemoglobin indicated that this environment also significantly reduced fatigue (p < 0.05) and moderately increased performance, compared to the high CCT LED light environment. These findings can serve as a springboard for further research that aims to develop interventions to reduce the effects of public health emergency lockdowns on mental and physical health in adolescents, and provide a reference for participants in the upcoming Asian Games and World University Games.

Lighting color temperature impacts effort-related cardiovascular response to an auditory short-term memory task

To better understand the impact of environmental light on processes that underlie cognitive activity, Lasauskaite and Cajochen (2018) recently proposed a theoretical model that predicts how light's correlated color temperature (CCT) affects effort. Here we tested whether the effects of CCT of light on effort-related cardiovascular response also extend to another sensory input—hearing. In two experimental blocks, participants were exposed to either low (2800 K) or high correlated color temperature (6500 K) light with an illumination level of 500 lux for 15 min before and while they performed an auditory n-back task varying in difficulty level (low difficulty/1-back vs. moderate difficulty/2-back). Mental effort was indexed as sympathetic beta-adrenergic impact on the heart, measured via cardiac pre-ejection period and systolic blood pressure. Based on the theoretical model, we hypothesized that light with a high CCT should lead to lower mental effort compared to light with a low CCT in both the low and moderate task difficulty conditions. Moreover, moderate task difficulty should lead to stronger effort compared to an easy task. The results did not show expected differences in invested effort levels between the task difficulty conditions (1-back vs. 2-back task) measured by cardiac pre-ejection period and systolic blood pressure. However, in line with our prediction, the results indicated that higher CCT of light decreased effort during an auditory memory task. Task performance was higher in easy than moderate task difficulty but was not altered by lighting conditions. Furthermore, we found no significant associations between cardiovascular reactivity and changes in mood, sleepiness, light, task, or effort ratings. Taken together, our results provide first evidence that higher CCT of light reduces the amount of effort invested during cognitive tasks for which hearing is needed. Given that this study was conducted under controlled laboratory conditions and with healthy young participants, additional research is needed to demonstrate that our results generalize to real-life applications. Nevertheless, we recommend that lower CCT of light should be avoided in learning and work contexts, as it might lead to higher effort and cardiovascular reactivity that may contribute to the development of cardiovascular health problems. Instead, we recommend higher CCT of light during daytime for wellbeing and health.

Synthesis of Efficient and Stable Tetrabutylammonium Copper Halides with Dual Emissions for Warm White Light-Emitting Diodes.

In order to achieve high color rendering index (CRI) and low correlated color temperature (CCT) indoor lighting, single component phosphors with broadband dual emission emission are high demanded for white light emitting diodes (WLEDs). However, phosphors with such fluorescent properties are rare at present. Herein, we report a facile solid-state chemical method for the synthesis of single-component phosphor with broadband emission and large Stokes shift that can meet the requirements of future white light sources. These new tetrabutylammonium copper halides phosphors have excellent warm white emission characteristics, and their luminescence peaks located at 494 nm and 654 nm, respectively. The optimized photoluminescence (PL) quantum yield can reach 93.7%. The typical CIE coordinate of the as-fabricated WLED is at (0.3620, 0.3731) with CRI of 89 and low CCT of 4516 K.

Single-component electroluminescent white light-emitting diodes based on zinc oxide quantum dots with high color rendition and tunable correlated color temperature

Single-component WLEDs with tunable CCT from 3303 to 8055 K and very high CRI &gt;90 have been realized using ZnO-QDs as emissive layer, which opens up a new avenue for the development of low-cost, environment-friendly, and high-performance single-component WLEDs.

Effect of Amorphous Photonic Structure Surface Mounted on Luminous Performances of White LED

We fabricated amorphous photonic structures (APSs) with different periods and hole diameters. The GaN-based white light emitting diodes (LEDs) at nominal correlated color temperatures (CCTs) of 5000 and 6000 K were surface mounted by these APSs. The electroluminescence (EL) measurements showed less luminous efficiency (LE) and higher CCT than the ones of the virginal white LEDs. However, the LEs of many APS-mounted white LEDs increased compared to white the LEDs without APSs at the same CCTs. A finite-difference time-domain (FDTD) simulation was carried out on the ASPs surface-mounted white LEDs and bidirectional scattering distribution functions (BSDFs) of different emissions were transferred to a Monte Carlo ray tracing simulation. The simulated LEs and CCTs conformed well to the experimental ones. The effects of the blue emission transmission and phosphor concentration were simulated to predict the absolute LE enhancement methods for white LEDs. At last, the hopeful APSs for high Les’ general lighting were discussed.

Effects of correlated color temperature of light on thermal comfort, thermophysiology and cognitive performance

Anecdotal evidence suggests that the correlated color temperature (CCT) of light can affect thermal comfort. Previous literature mostly investigated this effect over a short duration (<1 h) and often attributed it to the hue-heat hypothesis (color-temperature association), which posits that the visual experience of blue colors (high CCT) results in a cooler temperature sensation than red/yellow colors (low CCT) do. However, with longer duration, non-visual effects of CCT that elicit physiological changes may be at play additionally. Therefore, we contrasted two CCTs with relatively long exposures (>2 h; 2700 K vs. 5700 K with 500 lux illuminance at the eye) in office-like settings during mild cold exposure (17 °C) using a within-subject design (N = 16). The results indicate that CCT did not significantly affect thermal sensation in mild cold, which may be explained by the large interindividual variation in the color-temperature association. Interestingly, 5700 K even improved thermal comfort, decreased perceived shivering, and, after 1-h exposure, increased energy expenditure. Moreover, visual comfort was not significantly moderated by CCT, but 5700 K improved comprehensive cognitive performance. Concurrently, arousal and alertness were higher in 5700 K, potentially indicating greater non-visual effects in 5700 K. Further analysis revealed that thermal comfort significantly correlated with perceived shivering and visual comfort, but not with the color sensation of the light. Together, the results provide no support for the hue-heat hypothesis under mildly cold conditions and suggest that high CCT enhanced thermal comfort, alertness, arousal, and cognitive performance, likely via non-visual mechanisms that built up over longer exposure durations.

Improving white light emission and quantum yield of Ce@Eu co‐doped silicate glass by reducing Eu3+ to Eu2+ with Si3N4

AbstractRare‐earth‐doped transparent glass shows great potential in white light‐emitting diodes (wLEDs) application due to its excellent optical and luminous properties. Currently reported commercial wLEDs have a drawback in red emission missing, which leads to a relatively low color rendering index (CRI) and a relatively high correlated color temperature (CCT). In this work, Ce@Eu Sr–Si–O glass is fabricated using a high‐temperature quenching method. The white light is available when the ratio of Ce3+/Eu3+ equals 1, and the emitting color can be adjusted from blue to red by controlling the ratio of Ce3+/Eu3+. To further optimize the white light, Eu3+ ions can be reduced to Eu2+ according to the reaction of 6Eu3+ + 2N3− → 6Eu2+ + N2↑ by introducing Si3N4. As a result, the standard white light emission can be achieved in the Ce@Eu silicate glass contributed by the blue light from Ce3+, red light from Eu3+, and yellow–green light from Eu2+ (two elements, three emission). This glass shows excellent luminous properties, such as a color coordinate is (0.3651, 0.3269) in CIE 1931 color coordinate diagram, a CRI is over 70, a high quantum yield of 36.02%, and a CCT of 4117 K.

CsPbI3/N-GQDs dual layer phosphor-converted white-LEDs with ultrahigh luminous efficiency and color rendering index

Phosphor-converted LEDs or pc-LEDs, as a solid-state lighting source, are attractive for next-generation display technologies because of their energy savings, and green environmentally friendly nature. Recently, white LEDs are being produced commercially by coating blue LED (440–470 nm) chips with various yellow-emitting phosphors. However, the LEDs produced by this technique often exhibit high correlated color temperature (CCT) and low color rendering index (CRI) values, due to sufficient red spectral components not being present, and thus aren’t suitable for commercial grade white illumination. To circumvent this drawback, our work reports for the first time the use of blue and green-emitting nitrogen-functionalized graphene quantum dots (GQDs) coupled with red-emitting CsPbI3 NCs for phosphor-based LED applications. We deployed near-UV to visible excitable red-emitting perovskite CsPbI3 nanocrystals which contribute toward the red spectral component, thus greatly improving the CRI of the LEDs. CsPbI3 nanocrystals are optically excited by nitrogen-functionalized GQD with blue and green emissions in a remote double-layer phosphor stack technique. This double phosphor layer stacking greatly improves both the CRI and luminous efficiency of radiation (LER), which usually has a trade-off in previously reported phosphor stacks. A CCT of ∼5182 K providing daylight white tonality, with superior CRI (∼90%) and ultrahigh LER (∼250 lumens/watt) are reported, which are significantly higher than the established benchmarks.