Color Temperature Of Light Research Articles

(Invited) Full Spectrum White LEDs of Any Color Temperature with Color Rendering Index Higher Than 90 Using a Single Broad-Band Phosphor

A new phosphor alloy Ca1+xSr1-xGa2S3F2: Ce3+, Eu2+ with x = 0.04 exhibits a full spectrum emission in the entire visible wavelength range from 420 to 700 nm when excited by a LED chip with 400 nm emission. By simply depositing varying thicknesses (amount) of this phosphor powder on a 400 nm excitation LED source, white LEDs with correlated color temperatures (CCT) between 1700 K and 20,000 K and (x,y) chromaticity coordinates lying on the Planckian locus of the CIE chromaticity diagram has been demonstrated. To the best of our knowledge, this is the first report on the demonstration of a single full spectrum phosphor based white LEDs exhibiting the entire gamut of white light color temperature with CRI exceeding 90. Specifically CRI greater than 95 is reported for the CCT range of 2200 K – 8500 K.

Occupant response to different correlated colour temperatures of white LED lighting

Correlated Colour Temperature (CCT) of lighting may affect not only occupant visual perception, but also other indoor environment perceptions, such as perceptions of the thermal environment or the air quality. This study aimed at quantifying the association between CCT of white LED lighting and subjective perceptions and performance at operative temperatures at the upper and lower borders and in the middle of the comfort range.Higher CCT was significantly associated with decreasing thermal sensation, but only at the thermally neutral condition. Female subjects responded stronger to changes in CCT than male subjects. Under all temperature conditions, CCT was clearly associated with the perceived brightness of the light, and at 22 °C also with the perceived air quality and with subjectively assessed alertness. CCT had no effect on the measured performance of a d2 task.At 22 °C, the observed decrease in thermal sensation when CCT went from 2700 K to 6200 K was equivalent to a difference in operative temperature of 1.7 °C. With an assumed neutral CCT of 4500 K (middle of range), a decreased heating set point in an office building, corresponding to an equivalent shift in CCT from 4500 K to 2700 K, resulted in a reduction of around 8% of the building's total annual energy use. However, this assumes ideal conditions without influence from daylight, light from PC monitors, or coloured surfaces and other potentially disturbing factors.

Smart LED high CRI lighting systems

PurposeThe purpose of this paper is to present issues related to the design of a modern lighting system based on LED technology. The developed system provides lighting with a high colour rendering index (up to 98); it also has many innovative functions, which make its implementation bring significant energy savings and increase the comfort of work.Design/methodology/approachIn contrast to typical solutions, the dynamic synthesis of white light from six component colours was used in the presented project. This process is controlled by a microcontroller, and there is a colour temperature sensor in the feedback loop. The communication between smart luminaires and sensor modules is provided by means of a ZigBee wireless network.FindingsThe correctness of the proposed methodology has been proved by measurements and laboratory tests.Research limitations/implicationsThe process of improving the lighting system is continued and significant changes in the spectrum of used sensors are expected.Practical implicationsThe proposed system based on mixing light from six components is an innovative solution that besides undoubted advantages entails a more elaborate electronic circuitry. However, good characteristics of the obtained light, as well as the possibility of compensating for changes in colour temperature of natural light and reducing the impact of aging of LEDs, in the authors’ opinion, make the proposed solution find its place on the market.Originality/valueThe proposed solution is original, both in terms of the light mixing technique and advanced functionality offered by the system.

Off‐grid: solar powered LED illumination impacts epigeal arthropods

Abstract Advances in LED technology combined with solar, storable energy bring light to places remote from electricity grids. Worldwide more than 1.3 billion of people are living off‐grid, often in developing regions of high insect biodiversity. In developed countries, dark refuges for wildlife are threatened by ornamental garden lights. Solar powered LEDs (SPLEDs) are cheaply available, dim, and often used to illuminate foot paths, but little is known on their effects on ground living (epigeal) arthropods. We used off‐the‐shelf garden lamps with a single ‘white’ LED (colour temperature 7250 K) to experimentally investigate effects on attraction and nocturnal activity of ground beetles (Carabidae). We found two disparate and species‐specific effects of SPLEDs. (i) Some nocturnal, phototactic species were not reducing activity under illumination and were strongly attracted to lamps (>20‐fold increase in captures compared to dark controls). Such species aggregate in lit areas and SPLEDs may become ecological traps, while the species is drawn from nearby, unlit assemblages. (ii) Other nocturnal species were reducing mobility and activity under illumination without being attracted to light, which may cause fitness reduction in lit areas. Both reactions offer mechanistic explanations on how outdoor illumination can change population densities of specific predatory arthropods, which may have cascading effects on epigeal arthropod assemblages. The technology may thus increase the area of artificial light at night (ALAN) impacting insect biodiversity. Measures are needed to mitigate effects, such as adjustment of light colour temperature and automated switch‐offs.

Evaluating the influence of ambient light on scanning trueness, precision, and time of intra oral scanner

PurposeThis study evaluated the influence of illuminance and color temperature of ambient light on the trueness, precision, and scanning time of a digital impression. MethodsMaster data were acquired with a high-accuracy coordinate-measuring machine. The illuminance of ambient light was set at 0lux, 500lux, and 2500lux with a light-emitting diode (LED). Using a conversion filter, the color temperature was set at 3900 Kelvin (K) (yellow), 4100K (orange), 7500K (white), and 19,000K (blue). There were thus a total of 12 possible lighting conditions. The reference model was scanned five times under each condition by an intraoral scanner. Trueness was calculated as the mean difference between the master data and experimental data. Precision was calculated as the mean difference between the repeated scans in each test group. Statistical analysis was performed with two-way analysis of variance (ANOVA) and post hoc Tukey’s multiple comparison test. The significance level was 0.05. ResultsFor trueness, the mean deviation was significantly lower at 500lux than at 0lux and 2500lux. At 500lux, the mean deviation was significantly lower at 3900K than at other temperatures. Regardless of the color temperature, the scanning time was significantly longer at 2500lux than at other illuminance levels. ConclusionsThe 3900K and 500lux condition is the most appropriate lighting condition for taking a digital impression. This condition is typical of clinical settings. High illuminance ambient light increased the scanning time.

차량실내 활동별 조명의 조도와 색온도에 따른 탑승자의 심리생리적 반응

An experiment was carried out to investigate the effects of color temperature of in-vehicle lighting on passengers' psychophysiological responses in different activities. The illuminance of lighting was specified to 13.2, 62.0, and 26.0lx for resting, reading, and watching activities respectively, and 4 color temperatures(2700, 3700, 4700, and 5700K) were applied to each activity. The electroencephalogram, electrocardiogram, and electro-dermal activity were measured as the passengers' physiological responses. The results showed no difference in EEG, but ECG and EDA revealed a significant difference at 2700 and 3700K in some measures of resting and reading activities implying such color temperatures could help physical stability and relaxation. However, when a color temperature preference as a psychological response was questioned, 3700 and 4700K were tend to be selected although it differs according to the activities. It was slightly different from the bio-signal results, therefore the discrepancy was discussed in term of the familiarity to lighting color temperature.

Performance enhancement of white LED with TAG-Al2O3:Ce eutectic phosphor by partial Gd ion substitution

In the traditional white LED, the phosphor is combined with the blue LED chip after mixed with the resin composite material. This combination affects the final light efficiency and color temperature, and cannot provide long-term stable work because of high emission and high temperature. Based on Tb3Al5O12-Al2O3:Ce (TAG-Al2O3:Ce) eutectic, we developed the eutectic Tb1.5Gd1.5Al5O12-Al2O3:Ce ((TG) AG-Al2O3:Ce) to overcome the shortcomings of traditional phosphors. The eutectic was grown by an optical floating zone method. X-ray diffraction shows that the structure of (TG) AG-Al2O3 do not have significant changes compared to TAG-Al2O3, and the doped Ce3+ ions do not influence the basic structure of eutectic. Scanning electron microscopy shows that these materials have typical eutectic structure of sapphire and garnet phases, which can increase the length of the optical path to reduce the reflection loss and cause a higher luminous efficiency compared to the resin phosphor. Photoluminescence emission and excitation properties of (TG) AG-Al2O3 eutectic were investigated. The main excitation is in the luminous range (450 nm to 480 nm) of the blue LED chip for white LED. Compared with TAG-Al2O3:Ce, the emission peak is slightly shifted to the red, which cause the color temperature of (TG) AG-Al2O3:Ce eutectic LED is closer to natural light. The luminous efficiency of (TG) AG-Al2O3:Ce eutectic white LED is much higher than that of TAG-Al2O3:Ce eutectic. These results show that (TG) AG-Al2O3: Ce eutectic is promising phosphor for white LEDs.

Evaluation of Color Perception in Different Correlated Color Temperature of LED Lighting

Renk ve isik, ic mimarlik alaninda tasarimin temel unsuru olan ayrilmaz nesnelerdir. Isik degistiginde, algilanan ic mekânin yuzey renk gorunumu de degisir. Renk algisindaki bu degisim, yalnizca bir isik kaynagi turune veya aydinlatma yogunluguna degil, ayni zamanda bir isik kaynaginin renk sicakligina da baglidir. Bu calismanin amaci, LED aydinlatmanin farkli renk sicakligindaki renk algisini nasil etkiledigini anlamaktir. LED aydinlatmanin iki farkli sicak (2700o K) ve soguk (4000o K) renk sicakligi altinda asil renkler ile algilanan renk egilimlerini karsilastirmak amaciyla bir calisma yurutulmustur. Bu calismada, asil renkler ile algilanan renkler arasindaki olasi egilimleri ve kaliplari ortaya cikarmak icin Dogal Renk Sistemi (NCS), bir renk notasyon sistemi olarak kullanilmistir. LED aydinlatmanin her iki 2700o K ve 4000o K renk sicakligi altinda algilanan renkler icin genel egilimlerde, her bir asil renk icin nuans (rengin degeri ve doygunlugu) renk alaninda benzer desenleri ortaya cikarmis ve renk turu renk alaninda dagilma gostermistir.

The Effect of Lighting the Buildings on the Perception of People from the Color Temperature of Light

Considering the exclusive position of lighting in life and especially in the night lives of towns, presenting some principles to optimize the lighting procedures of contemporary buildings and historical edifices are of utmost importance in urban matters. There are several standards for colors and lights to be used in the interiors of buildings, but not so many principles can be found for the exteriors and facades of buildings. Moreover, in the lighting of buildings, mostly matters such as functionality, aesthetics, and security issues have been taken into account while issues such as optimum energy use and visual perception have been neglected. In the present study, the above mentioned matters as well as the sense of relief induced by the lighting and its colors have been investigated; the latter point brings about reduced energy use in different seasons. The respondents in this study did not regard the temperature of the colors and answered the questionnaire according to the feelings they got from the colors. The results show that individuals get a feeling of warmth from colors such as white, red, orange, and yellow; this finding can be used to change the lighting of buildings to warm colors throughout cold seasons. Furthermore, the respondents reported a feeling of cold from colors like cold white, blue, and purple; accordingly, this finding can be used in warm seasons, especially in areas with hot and dry weather. The application of cold colors in such areas can reduce the amount of used energy. In addition, in order to apply a lighting project and use the facilities of artificial lighting, one must acquire the required knowledge of its technicalities and facilities; then, these facilities are to be evaluated through technical factors so that a proper optimized pattern for providing aesthetics as well as visual relief along with reduced energy use can be proposed.

A Study on User-Centered Emotional Illumination Design Using Color Temperature of Light

A Study on User-Centered Emotional Illumination Design Using Color Temperature of Light

The Effect of Lighting the Buildings on the Perception of People from the Color Temperature of Light

Considering the exclusive position of lighting in life and especially in the night lives of towns, presenting some principles to optimize the lighting procedures of contemporary buildings and historical edifices are of utmost importance in urban matters. There are several standards for colors and lights to be used in the interiors of buildings, but not so many principles can be found for the exteriors and facades of buildings. Moreover, in the lighting of buildings, mostly matters such as functionality, aesthetics, and security issues have been taken into account while issues such as optimum energy use and visual perception have been neglected. In the present study, the above mentioned matters as well as the sense of relief induced by the lighting and its colors have been investigated; the latter point brings about reduced energy use in different seasons. The respondents in this study did not regard the temperature of the colors and answered the questionnaire according to the feelings they got from the colors. The results show that individuals get a feeling of warmth from colors such as white, red, orange, and yellow; this finding can be used to change the lighting of buildings to warm colors throughout cold seasons. Furthermore, the respondents reported a feeling of cold from colors like cold white, blue, and purple; accordingly, this finding can be used in warm seasons, especially in areas with hot and dry weather. The application of cold colors in such areas can reduce the amount of used energy. In addition, in order to apply a lighting project and use the facilities of artificial lighting, one must acquire the required knowledge of its technicalities and facilities; then, these facilities are to be evaluated through technical factors so that a proper optimized pattern for providing aesthetics as well as visual relief along with reduced energy use can be proposed.

The impact of fluorescent and led lighting on students attitudes and behavior in the classroom

Introduction: This study examined empirical research on the effects of high correlated color temperature light-emitting diodes (LED) and fluorescent lighting on students in the classroom. LED is becoming the most recent lighting option for optimal energy efficiency over fluorescent technology. Background: A review of the literature indicates correlated color temperature (CCT) of lighting has non-visual effects on students, with higher CCT positively impacting attitudes and behavior. The review also revealed current studies regarding dynamic or tunable lighting that adjusts CCT based on desired activity and mood. Data from an original survey analyzed teacher insights and perceptions regarding student attitudes and behaviors associated with existing classroom lighting and the impact of higher color temperature LED. Methods: Participants were pre-K through high school qualified teachers from three schools and/or personal contacts of the principal investigator. Seventy-five teachers responded to the online questionnaire. The survey data suggests teachers perceive higher color temperature lighting positively impacts student alertness, attitude, and energy level; and adjusting light levels throughout a school day positively impacts student engagement. Results and conclusion: Results supported the perception of higher correlated color temperature lighting positively impacting alertness, attitude, and energy level. Findings also supported the ability to change light levels throughout the school day to positively impact student engagement and mood. There were mixed results regarding higher correlated color temperature impacting attention and on-task/off- task behaviors. Results regarding the impact of sound and flickering from fluorescent lights were not significant.

A note on dispersion phenomenon in the fiber daylighting system with the Fresnel lens

During practical operation, it is found that the color temperature of output flux of the fiber daylighting system with the Fresnel lens decreased severely under solar tracking error, which damages the quality of daylighting. A series of measurements on spectrum and ray tracing simulations on concentration process were designed and carried out. The data indicate that the decrease of the color temperature is a result of a chain reaction. The dispersion of the Fresnel lens, the interference of the secondary concentrator on the incident angle of the light and the attenuation characteristics of the fiber cause the reduction of the output light color temperature.

Cool white light emission from the yellow and blue emission bands of the Dy(III) complex under UV-excitation

A pyrazine as ancillary ligand coordinated to dysprosium(III) tris-acetylacetonate complex was synthesized and thoroughly characterized. Photophysical properties of the Dy(III) complex were investigated both in solution and solid powder. The quantum yield (ɸ) of the complex in chloroform is 0.024. The UV excitation of the complex in the solid state generates white light emission which indicates significant energy transfer from the ligands (acetylacetone and pyrazines) to the Dy(III) ion. This could be due to the appropriate balancing of the intensity ratio of the yellow and blue emission bands of the Dy(III) complex. This represents an example of a single component system. The correlated colour temperature (CCT) of this white light is calculated as 5340.21 K which lies in a cool region. The radiative properties of the Dy(III) complex are calculated using Judd-Ofelt analysis and the phenomenological parameters calculated are Ω2 = 8.07 × 10−20 cm2, Ω4 = 1.94 × 10−20 cm2 and Ω6 = 1.67 × 10−20 cm2. The branching ratio (βR) ratio calculated from the emission spectrum follows the order: 4F9/2 → 6H13/2 > 4F9/2 → 6H15/2 > 4F9/2 → 6H11/2. The βR for the 4F9/2 → 6H13/2 transition is highest, and it contributes 83% to the total emission branching and can be considered as a possible transition for laser amplification. The white light emission from the solid powder Dy(III) complex as a single component may possibly find its use in white light emitting devices (WLEDs).

Correlated colour temperature of morning light influences alertness and body temperature

Though several studies have reported human alertness to be affected by the intensity and spectral composition of ambient light, the mechanism behind this effect is still largely unclear, especially for daytime exposure. Alerting effects of nocturnal light exposure are correlated with melatonin suppression, but melatonin levels are generally low during the day. The aim of this study was to explore the alerting effect of light in the morning for different correlated colour temperature (CCT) values, as well as its interaction with ambient temperature. Body temperature and perceived comfort were included in the study as possible mediating factors. In a randomized crossover design, 16 healthy females participated in two sessions, once under 2700K and once under 6500K light (both 55lx). Each session consisted of a baseline, a cool, a neutral and a warm thermal environment. Alertness as measured in a reaction time task was lower for the 6500K exposure, while subjective sleepiness was not affected by CCT. Also, core body temperature was higher under 6500K. Skin temperature parameters and perceived comfort were positively correlated with subjective sleepiness. Reaction time correlated with heat loss, but this association did not explain why the reaction time was improved for 2700K.

공용화장실에서 적정 조도 및 색온도 범위 도출

A Public toilet is the sanitary space, which is installed for public citizens or guardians, or customers so that they can wash hands, or relieve themselves, and it is installed alone or as a part of a building. It is used widely from young kids to the elderly. In the private space where an individual lives, personalized lighting design could be made, but in case of the public space where many and unspecified persons use, it’s necessary to arrange the lighting design reflecting the common visual properties, and sensibility reaction of all ages. Accordingly, This study intended to deduct the optimum color temperature and illumination scope corresponding to majors of toilet uses in their 20s～50s performed at a public toilet. As a result of the comprehensive analysis, it was found that 400lx in illumination of 4,000～5,000K in color temperature was the most optimal as the lighting environment for a public toilet. In addition, it was found that there was no difference between the illumination and color temperature of lighting by behavior. This study deducted the evaluation result targeting the age groups in their 20s～30s, and 40s～50s.

CIE1931xy 색도도를 이용한 LED 조명의 색온도와 파장

본 논문에서는 스마트폰을 메인 제어장치로 사용하여 색온도와 파장을 제어할 수 있는 휴먼조명과 특수조명의 기능을 갖는 LED 조명장치를 설계 및 구현하였다. 구현 방법으로는 CIE1931 xy 색도도의 색좌표 값을 이용하여 LED 조명의 색온도과 파장을 제어하는 방법을 사용하였다. 그리고 구현 알고리즘은 McCamy의 색온도 변환 알고리즘을 적용하였다. 성능검증은 ANSI C78.377A를 적용하였으며, 검토결과 색좌표 평균 오차값 x=-0.006, y=-0.008값과 평균 색온도 149.385K의 오차가 발생하였지만 ANSI C78.377A의 허용범위를 만족하였다. 파장은 Red LED의 평균 0.5nm의 오차값, Green LED의 평균 –0.1nm의 오차 값, Blue LED의 평균 1.0nm의 오차 값으로 검토되어 규격서와 큰 차이 없는 값을 얻을 수 있었다. 그 결과로 기존의 LED 조명은 각각 사용목적에 맞게 제작하였으나 제안된 방법을 사용하면 휴먼조명과 특수조명을 하나로 통합한 LED 조명장치의 색 온도와 파장을 제어 할 수 있다.

Influence of lighting color temperature on effort-related cardiac response

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.

Full Spectrum White LEDs of Any Color Temperature with Color Rendering Index Higher Than 90 Using a Single Broad-Band Phosphor

A new phosphor alloy Ca1+xSr1-xGa2S3F2: Ce3+, Eu2+ with x = 0.04 exhibits a full spectrum emission in the entire visible wavelength range from 420 to 700 nm when excited by a LED chip with 400 nm emission. By simply depositing varying thicknesses (amount) of this phosphor powder on a 400 nm excitation LED source, white LEDs with correlated color temperatures (CCT) between 1700 K and 20,000 K and (x,y) chromaticity coordinates lying on the Planckian locus of the CIE chromaticity diagram has been demonstrated. To the best of our knowledge, this is the first report on the demonstration of a single full spectrum phosphor based white LEDs exhibiting the entire gamut of white light color temperature with CRI exceeding 90. Specifically CRI greater than 95 is reported for the CCT range of 2200 K – 8500 K.

Lighting of a cardiac intensive care unit: Emotional and visual effects on patients and nurses

This study discusses the emotional and visual effects of the luminous environment of cardiac intensive care units on both patients and nurses. We draw the following conclusions: (1) the light level, colour temperature, and lighting design all affect the satisfaction of both patients and nurses. (2) Although patients prefer a low colour temperature, nurses prefer a high colour temperature. The influence of colour temperature on the satisfaction of patients and nurses is smaller than factors such as light level and light distribution. (3) Major factors affecting patient satisfaction consist of an emotional factor and a visual factor in inverse correlation under several particular influences. (4) Nurse satisfaction approximates the visual factor score. (5) The visual factor scores of the subjects (patients and nurses) are in apparent positive correlation with light level. (6) In a scenario characterized by an illuminance of 200 lx, the trends in patients’ emotional factor and visual factor intersect where the emotional factor peaks. However, when the illuminance and average luminance grow further, the emotional factor score decreases.