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The influence of light spectral properties on circadian rhythms is of substantial interest to laboratory-based investigation of the circadian system and to field-based understanding of the effects of artificial light at night. The trade-offs between intensity and spectrum regarding masking behaviors are largely unknown, even for well-studied organisms. We used a custom LED illumination system to document the response of wild-type house mice (Mus musculus) to 1-h nocturnal exposure of all combinations of four intensity levels (0.01, 0.5, 5 and 50 lx) and three correlated color temperatures (CCT; 1750, 1950 and 3000 K). Higher intensities of light (50 lx) suppressed cage activity substantially, and consistently more for the higher CCT light (91% for 3000 K, 53% for 1750 K). At the lowest intensity (0.01 lx), mean activity was increased, with the greatest increases for the lowest CCT (12.3% increase at 1750 K, 3% increase at 3000 K). Multiple linear regression confirmed the influence of both CCT and intensity on changes in activity, with the scaled effect size of intensity 3.6 times greater than that of CCT. Activity suppression was significantly lower for male than for female mice. Assessment of light-evoked cFos expression in the suprachiasmatic nucleus at 50 lx showed no significant difference between high and low CCT exposure. The significant differences by spectral composition illustrate a need to account for light spectrum in circadian studies of behavior, and confirm that spectral controls can mitigate some, but certainly not all, of the effects of light pollution on species in the wild.

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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.

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Diaphanoscopic illumination has the disadvantage that the intraocular spectrum is red-shifted due to transmission properties of the eyewall. This red-shift should be counteracted as well as the retinal risk should be reduced with adjusting the spectral distribution of the illumination light. Likewise, the illumination spectrum has to be adapted to the eye color of the patient. With the further development of a red, green, blue and white light-emitting diode (RGBW-LED) diaphanoscopy pen, the intensities of each color can be varied. The functionality of the LED pen is tested on ex-vivo porcine eyes. By measuring the transmission of the sclera and choroidea, the photochemical and thermal retinal hazard and the maximum exposure time are determined according to the standard DIN EN ISO 15004-2:2007. With this RGBW-LED pen the intraocular space can be illuminated clearly of up to 1.5 h without potential retinal damage according to DIN EN ISO 15004:2-2007. By adjusting the illumination spectrum the red-shift can be compensated and retinal risk can be reduced. By varying the LED intensities, the correlated color temperature in the eye can also be varied from cold white to warm white appearance as comfortable to the ophthalmologist. Additionally, a simple adjustment of the illumination to the eye color of the patient is possible. Using this RGBW-LED pen, the ophthalmologist can set the desired intraocular color appearance, which he prefers for special applications. He could also adjust the illumination to the eye color as this would reduce retinal hazard.

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Lipstick is one of the most commonly used cosmetics, which is closely associated with female attractiveness and influences people's perception and behavior. This study aimed to investigate the impact of light sources, lipstick colors, as well as gender on the subjective assessment of lipstick color products from the prospective of color preference, purchase intention and sexual attractiveness. The correlation between color preference evaluations when applying lipstick on lips and on forearms was also explored. Sixty participants completed their visual assessment of 15 lipsticks worn by 3 models under 5 light sources, with uniformly sampled correlated color temperature (CCT) values ranging from 2,500 K to 6,500 K. The results indicated that the light source significantly influenced color preference and purchase intention, while lipstick color significantly impacted on sexual attractiveness. The interactions between gender and other factors were also observed and are discussed. Compared to men, women were found to be more sensitive to different light sources and hold different attitudes toward different lipstick colors under different CCTs. Interestingly, no significant correlation was found between lipstick color preference ratings on the lips and forearm, which conflicted with the commonly recognized way of lipstick color selection. These findings should contribute to a deeper understanding of the consumer attitude toward lipstick colors and provide a useful reference for lighting design in situations where cosmetics are specified, manufactured, retailed and generally used, both professionally and in the home.

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(1) Background: In ophthalmic surgery, white light is mostly applied to illuminate the intraocular space, and ophthalmologists are comfortable working with it. Diaphanoscopic illumination changes the spectral composition of light, resulting in a change in the correlated color temperature (CCT) of the intraocular illumination. This color change makes it difficult for surgeons to recognize the structures in the eye. CCT during intraocular illumination has not yet been measured before, and it is the aim of this study to perform such measurement. (2) Methods: CCT was measured inside ex vivo porcine eyes during diaphanoscopic illumination and endoillumination using a current ophthalmic illumination system with a detection fiber inside the eye. By applying pressure on the eye with a diaphanoscopic fiber, the dependency of CCT on pressure was examined. (3) Results: The intraocular CCT values during endoillumination were 3923 K and 5407 K for the halogen and xenon lamps, respectively. During diaphanoscopic illumination, a strong unwanted red shift was observed, resulting in 2199 K and 2675 K for the xenon and the halogen lamps, respectively. Regarding different applied pressures, the CCT did not differ considerably. (4) Conclusions: This red shift should be compensated for in the development of new illumination systems since surgeons are used to white light illumination, which also simplifies the identification of retinal structures.

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From the perspective of psychophysiological evaluation, this paper provides a theoretical reference for the lighting settings of museums. In order to study the impact of correlated color temperature (CCT) on visitors' perception and preference in museum exhibitions, an experiment was conducted in the ergonomics laboratory of Nanjing Forestry University. We invited 50 participants to visit the virtual reality museum exhibitions with different CCTs, built by Autodesk 3D's Max 2017. Specific psychophysiology variables-eye movement, electrodermal activity (EDA), and heart rate variability (HRV)-and the perception and preference of participants were collected. The results indicated that the association of CCT with eye movement, HRV, and some perceptual dimensions was significant. Under high illumination conditions with different CCTs, the pupil diameter and warmth decreased with the increase in CCT, but the comfort and pleasure scores increased first and then decreased. The CCT scenes sorted by LF/HF ratio from high to low were 4500 K, 6000 K, and 3000 K, which was consistent with the results of preference ranking. The LF/HF ratio showed significant sex differences and major discrepancies.

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Spectral optimization is applied as an effective tool in designing solid-state lighting devices. Optimization speed, however, has been seldomly discussed in previous reports as regards designing an algorithm for white light-emitting diodes (WLEDs). In this study, we propose a method for trichromatic WLEDs to obtain the optimal Ra under target correlated color temperatures (CCTs). Blue-, yellow-, and red-color monochromatic spectra, produced by the GaN LED chip, YAG:Ce3+ phosphors, and CdSe/ZnSe quantum dots, respectively, are adopted to synthesize white light. To improve the effectiveness of our method, the concept of dual weight coefficients is proposed, to maintain a numerical gap between the proposed floating CCT and the target CCT. This gap can effectively guarantee that Ra and CCT ultimately move toward the targeting value simultaneously. Mechanisms of interaction between CCT, Ra, and dual-weight coefficients are investigated and discussed in detail. Particularly, a fitting curve is drawn to reveal the linear relationship between weight coefficients and target CCTs. This finding effectively maintains the accuracy and accelerates the optimization process in comparison with other methods with global searching ability. As an example, we only use 29 iterations to achieve the highest Ra of 96.1 under the target CCT of 4000 K. It is hoped that this study facilitates technology development in illumination-related areas such as residential intelligent lighting and smart planting LED systems.

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Light plays an essential role in psychobiological and psychophysiological processes, such as alertness. The alerting effect is influenced by light characteristics and the timing of interventions. This meta-analysis is the first to systematically review the effect of light intervention on alertness and to discuss the optimal protocol for light intervention. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020181485), we conducted a systematic search of the Web of Science, PubMed, and PsycINFO databases for studies published in English prior to August 2021. The outcomes included both subjective and objective alertness. Subgroup analyses considered a variety of factors, such as wavelength, correlated color temperature (CCT), light illuminance, and timing of interventions (daytime, night-time, or all day). Twenty-seven crossover studies and two parallel-group studies were included in this meta-analysis, with a total of 1210 healthy participants (636 (52%) male, mean age 25.62 years). The results revealed that light intervention had a positive effect on both subjective alertness (standardized mean difference (SMD) = -0.28, 95% confidence interval (CI): -0.49 to -0.06, P = 0.01) and objective alertness in healthy subjects (SMD = -0.34, 95% CI: -0.68 to -0.01, P = 0.04). The subgroup analysis revealed that cold light was better than warm light in improving subjective alertness (SMD = -0.37, 95% CI: -0.65 to -0.10, P = 0.007, I2 = 26%) and objective alertness (SMD = -0.36, 95% CI: -0.66 to -0.07, P = 0.02, I2 = 0). Both daytime (SMD = -0.22, 95% CI: -0.37 to -0.07, P = 0.005, I2 = 74%) and night-time (SMD = -0.32, 95% CI: -0.61 to -0.02, P = 0.04, I2 = 0) light exposure improved subjective alertness. The results of this meta-analysis and systematic review indicate that light exposure is associated with significant improvement in subjective and objective alertness. In addition, light exposure with a higher CCT was more effective in improving alertness than light exposure with a lower CCT. Our results also suggest that both daytime and night-time light exposure can improve subjective alertness.

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Color and light are two ambient attributes for interior spaces that can be used in the design and modification of workspaces. The visual and psychological effects of color and light of each have been studied separately and widely. The aim of this study was to investigate the simultaneous effects of warm/cool white light on visual perception and mood in a simulated colored workspace. Thirty-three healthy male participants were recruited. They were asked to judge the visual perception and mood of three types of workspace that were designed by colors of white, red, blue, and lights of a cool and warm white in the random six sessions. The participants have experienced higher levels of tension, anger, depression, anxiety and lower levels of visual comfort, attractiveness, brightness and calmness of environment in the red condition than to white in both state of light. The blue wall reduced brightness and increased attractiveness of environment compared to white wall. Cool white light reduced the warmth of color and increased brightness in all three color environments compared to warm light. The preference for cool or warm light depends on the color of the environment's indoor surface. It seems that the combination of the white color and warm light or the blue color with cool light has a more favorable effect on visual perception and people's mood in workplaces.

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In this paper, a new method to regulate the correlated color temperature (CCT) of white light-emitting diodes (LEDs) is proposed for the single-chip packaging structure, in which the blue light distribution emitted from the chip in the red/yellow phosphor layer was modulated through changing the paraffin-polydimethylsiloxane (PDMS) film transparence and haze. The results show that the transmittance of the paraffin-PDMS film can be modulated from 49.76% to 97.64%, while the haze of that ranges from 88.19% to 63.10%. When the thickness of paraffin-PDMS film is 0.6 mm, and the paraffin-PDMS film concentration is 30 wt%, the CCT of white LED decreases from 15177 K to 3615 K with the increase of thermal load in the paraffin-PDMS film. The modulating range of its CCT reaches 11562 K. The maximum CCT variation at the same test condition is only 536 K in the repeated experiments within one week.

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The high blue proportion of phosphor-conversion white-light emitting diodes (pc-LEDs), especially of those with higher correlated color temperatures (CCT), raises concern about photochemically induced retinal damages. Although almost all general lighting service LEDs are safe, other applications exist, like spotlights for theatres or at construction sites, that can pose a severe blue-light hazard (BLH) risk, and their photobiological safety must be assessed. Because of required but challenging radiance measurements, a calculative approach can be supportive for risk assessment. It is the aim of this work to exploit Gaussian functions to study LED parameter variations affecting BLH exposure. Gaussian curve approximations for color LEDs, the BLH action spectrum, and the spectral luminous efficiency for photopic vision enabled analytically solving the BLH efficiency, ηB, and the BLH efficacy of luminous radiation, KB,v. It was found that sigmoidal functions describe the CCT dependence of ηB and KB,v for different color LEDs with equal spectral bandwidth. Regarding pc-LEDs, variations of peak wavelengths, intensities, and bandwidths led to linear or parabolic shaped chromaticity coordinate correlations. ηB and KB,v showed pronounced CCT dependent extrema that might be exploited to reduce BLH. Finally, an experimental test of the presented Gaussian approach yielded its successful applicability for color and pc-LEDs but a minor accuracy for blue and green LEDs.

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Comfortable light emitting diode (LED) lighting conditions were examined for psychological and physiological responses. Eight male and eight female subjects participated in a series of experiments. They were exposed to light emitted from LED lights of 3000 K in the ranges of 150-400 lux and 1500-5000 lux; 4000 K in the ranges of 140-640 lux and 2000-5000 lux; and 5000 K in the ranges of 70-270 lux and 2500-7000 lux. Illuminance at a given correlated color temperature was first maintained at the lowest value in the designated range and then increased in a stepwise manner. On reaching the highest value in the range, it was then decreased to the lowest value in a stepwise manner. The subjects were required to indicate their perception of brightness, glare, and comfort at the controlled illuminance levels. Electrocardiogram and electroencephalogram data were monitored continuously throughout exposure. The results showed that the boundary illuminances estimated from psychological and physiological responses did not significantly differ between male and female subjects, but differed markedly from those of fluorescent lights tested in a previous study. The high boundaries of the LED lights were higher than those of the fluorescent lights. The low boundaries of the LED lights at 3000 K and 4000 K were higher than those of the fluorescent lights, but the boundaries at 5000 K were lower than those of the fluorescent lights. These differences may be due to differences in the spectral distribution and luminance for a given illuminance between LED and fluorescent lights.

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Phosphors have been used as wavelength converters in illumination for many years. When it is excited with blue light, the frequently used yttrium aluminium garnet doped with cerium (YAG:Ce) phosphor converts a part of blue light to a wideband yellow light, resulting in the generated light having a white color. By combining an appropriate concentration of the YAG:Ce phosphor and blue excitant light, white light of a desired correlated color temperature (CCT) can be obtained. However, this type of illumination has a lower color rendering index value (CRI). In an attempt to improve the CRI value, we mixed the YAG:Ce phosphor with europium-doped calcium sulfide phosphor (CaS:Eu), which resulted in a considerably increased CRI value. This article examines an experiment with luminescent layers consisting of a mixture of selected phosphors and polydimethylsiloxane (PDMS). Different thicknesses in these layers were achieved by changing the speed of rotation during their accumulation onto laboratory glass using the method of spin coating. The spectral characteristics of these luminescent layers as they were excited with blue light emitting diode (LED) and laser diode (LD) were then determined. A suitable combination of the YAG:Ce phosphor with a phosphor containing europium, as it was excited with a blue LED, yielded a source of white light with a CRI value of greater than 85. The response time in the tested luminescent layers to a rectangular excitant impulse (generated by a signal generator and transmitted by LD) was also measured in order to examine their potential use in visible light communications (VLC).

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The luminescent solar concentrator (LSC) is a promising concept for the integration of photovoltaic (PV) generators into the building envelope. Having the form of semitransparent plates, LSCs offer a high degree of flexibility and can be used as windows or facades, as part of the of building-integrated photovoltaic (BIPV) industry. Existing performance characterizations of LSC devices focus almost exclusively on electric power generation. However, when used as window components, the transmitted spectrum can alter the color, potentially affecting the visual comfort of the occupants by altering the properties of the sunlight. In this study, eight different state-of-the-art nanocrystals are evaluated as potential candidates for LSC window luminophores, using Monte Carlo simulations. The transparency of each LSC window varies between 90% and 50%, and the color-rendering properties are assessed with respect to the color rendering index (CRI) and the correlated color temperature (CCT). It is found that luminophores with a wide absorption bandwidth in the visible spectrum can maintain a high CRI value (above 85) and CCT values close to the Planckian locus, even for high luminophore concentrations. In contrast, luminophores that only absorb partly in the visible spectrum suffer from color distortion, a situation characterized by low CCT and CRI values, even at high transmittance.

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Expanding the acceptable range of indoor temperatures allows to reduce building energy consumption and may be beneficial for health. Therefore, we explored whether light conditions can be used to influence thermal perception under various ambient temperatures. In two laboratory experiments, we tested the effect of the correlated color temperature of light (2700 K and 5800 K) and its intensity (5 and 1200 lux) on thermal perception. The light exposures were provided during cool, neutral, and warm thermal conditions. Cold-induced perceived shivering was higher for the 5800 K light exposure. All other parameters related to thermal perception did not significantly differ between the light exposures. Interestingly, the other way around, an increasing ambient temperature resulted in a warmer perception of the light color. In every light condition, it appeared that the perceived light intensity was closest to neutral under the thermoneutral condition. Between different light sessions, the change in visual comfort and the change in thermal comfort were positively related. The main conclusion therefore is that thermal discomfort can be partly compensated by lighting that results in a higher perceived visual comfort. Field studies are required to demonstrate whether lighting can enable new strategies to improve indoor environmental workplace satisfaction.

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Studies with monochromatic light stimuli have shown that the action spectrum for melatonin suppression exhibits its highest sensitivity at short wavelengths, around 460 to 480 nm. Other studies have demonstrated that filtering out the short wavelengths from white light reduces melatonin suppression. However, this filtering of short wavelengths was generally confounded with reduced light intensity and/or changes in color temperature. Moreover, it changed the appearance from white light to yellow/orange, rendering it unusable for many practical applications. Here, we show that selectively tuning a polychromatic white light spectrum, compensating for the reduction in spectral power between 450 and 500 nm by enhancing power at even shorter wavelengths, can produce greatly different effects on melatonin production, without changes in illuminance or color temperature. On different evenings, 15 participants were exposed to 3 h of white light with either low or high power between 450 and 500 nm, and the effects on salivary melatonin levels and alertness were compared with those during a dim light baseline. Exposure to the spectrum with low power between 450 and 500 nm, but high power at even shorter wavelengths, did not suppress melatonin compared with dim light, despite a large difference in illuminance (175 vs. <5 lux). In contrast, exposure to the spectrum with high power between 450 and 500 nm (also 175 lux) resulted in almost 50% melatonin suppression. For alertness, no significant differences between the 3 conditions were observed. These results open up new opportunities for lighting applications that allow for the use of electrical lighting without disturbance of melatonin production.

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Eu3+ doped and Dy3+ codoped yttrium oxide (Y2O3) phosphors have been prepared using solid-state reaction technique (SSR). The prepared phosphors were characterized by X-ray diffractometer (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM) and Fourier transforms infrared spectroscopy (FTIR) techniques. Photoluminescence (PL) and Thermoluminescence (TL) properties were studied in detail. PL emission spectra were recorded for prepared phosphors under excitation wavelength 254 nm, which show a high intense peak at 613 nm for Y2O3:Dy3+, Eu3+ (1:1.5 mol %) phosphor. The correlated color temperature (CCT) and CIE analysis have been performed for the synthesized phosphors. TL glow curves were recorded for Eu3+doped and Dy3+codoped phosphors to study the heating rate effect and dose response. The kinetic parameters were calculated using peak shape method for UV and γ exposures through computerized glow curve deconvolution (CGCD) technique. The phosphors show second order kinetics and activation energies varying from 5.823 × 10- 1 to 18.608 × 10- 1 eV.

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Higher color temperature refers to a higher proportion of blue spectral components of light, that are known to be associated with higher alertness state in humans. Based on motivational intensity theory (Brehm & Self, 1989), here we predicted that this lighting-induced alertness state should inform about the readiness to perform and this way influence subjective task demand and thus mental effort. To test this, study participants spent 15min under one of four lighting color temperature conditions and then performed a cognitive task. As predicted, effort-related cardiac response, indexed by a shortened cardiac pre-ejection period, decreased with increasing color temperature of light, as indicated by a significant single planned linear contrast. These results demonstrate that spectral properties of light can influence mental effort mobilization.

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Plants sharing a single light environment on a spaceship with a human being and bearing a decorative function should look as natural and attractive as possible. And consequently they can be illuminated only with white light with a high color rendering index. Can lighting optimized for a human eye be effective and appropriate for plants? Spectrum-based effects have been compared under artificial lighting of plants by high-pressure sodium lamps and general-purpose white LEDs. It has been shown that for the survey sample phytochrome photo-equilibria does not depend significantly on the parameters of white LED light, while the share of phytoactive blue light grows significantly as the color temperature increases. It has been revealed that yield photon flux is proportional to luminous efficacy and increases as the color temperature decreases, general color rendering index Ra and the special color rendering index R14 (green leaf) increase. General-purpose white LED lamps with a color temperature of 2700 K, Ra > 90 and luminous efficacy of 100 lm/W are as efficient as the best high-pressure sodium lamps, and at a higher luminous efficacy their yield photon flux per joule is even bigger in proportion. Here we show that demand for high color rendering white LED light is not contradictory to the agro-technical objectives.

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The spectroscopic and photoluminescence characteristics of trivalent dysprosium (Dy(3+))-doped Sr0.5Ca0.5TiO3 phosphor materials synthesized via solid-state reaction method were studied. The X-ray diffraction profile confirmed the orthorhombic perovskite structure of the prepared samples. Judd-Ofelt analysis was carried out to obtain the intensity parameters and predicted radiative properties of Sr0.5Ca0.5TiO3:2wt%Dy(3+). The photoluminescence spectrum of Dy(3+)-doped Sr0.5Ca0.5TiO3 showed three emission peaks at 481, 574 and 638 nm corresponding to (4)F9/2 →(6)H15/2, (4)F9/2 →(6)H13/2 and (4)F9/2 →(6)H11/2 transitions respectively. The variation of luminescence intensity with different excitation wavelengths and Dy(3+) concentrations is discussed. The decay profiles of (4)F9/2 excited levels of Dy(3+) ions show bi-exponential behaviour and also a decrease in average lifetime with increase in Dy(3+) concentration. Yellow to blue luminescence intensity ratio, CIE chromaticity co-ordinates and correlated color temperature were also calculated for different concentrations of Dy(3+)-doped Sr0.5Ca0.5TiO3 phosphor at different λex.

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