Dissertations / Theses on the topic 'Correlated colour temperature'

This thesis deals with luminance parameters measurement and ways to accomplish this using LabView software. The first part focuses on luminance parameters measurable by spectroradiometer and their meaning. Following part introduces reader to hardware equipment that is used in the measurement. Third part contains description of LabView software and explains what is required to make a communication between equipment and PC work. Next part explains how the communication with peripherals was achieved. Following up is the part where it is described how programs controlling AC and DC power supplies work. In this part the user interface is described.

This master's thesis deals with the search of commercially available luminance analysers and cameras that use the measurement of correlated colour temperature. It also deals with calculations of correlated colour temperature according to various available methods. The luminance analyser LDA-LumiDISP is based on a DSLR camera. The principle of its operation and possible errors in capturing pictures are discussed here. The work deals with extensive testing of the LDA-LumiDISP luminance analyser, which is primarily intended for measuring luminance in the set scene, but can also be used to measure the correlated colour temperature. The device is being tested in terms of measuring the correlated colour temperature in laboratory and field conditions. The result of the master's thesis is the calculation of measurements uncertainty for certain light sources and the optimization of the measuring algorithm to reduce them.

In this thesis we examine the feasibility of developing a white light source capable of producing colors between 2500 and 7500 Kelvin on the black-body radiator spectrum by simply adjusting amperage to a blue and ultraviolet (UV) light emitting diode (LED). The purpose of a lighting source of this nature is to better replicate daylight inside a building at a given time of day. This study analyzes the proposed light source using a 385 nm UV LED, a 457 nm blue LED, a 479 nm blue LED, a 562 nm peak cerium doped yttrium aluminum garnet (YAG:Ce) phosphor, and a 647 nm peak selenium doped zinc sulfide (ZnS:Se) phosphor. Our approach to this study initially examined optical performance of yellow-emitting phosphor (YAG:Ce) positioned at specific distances above a blue LED using polydimethylsiloxane (PDMS) as a substrate. An understanding of how phosphor concentration within the PDMS, the thickness of the PDMS, and how substrate distance from the LED die affected light intensity and color values (determined quantitatively by utilizing the 1931 CIE 2° Standard Observer) enabled equations to be developed for various lens designs to efficiently produce white light using a 457 nm peak wavelength LED. The combination of two luminescent sources (457 nm LED and YAG:Ce) provided a linear trend on the 1931 CIE diagram which required a red illumination source to obtain Kelvin values from 2500 to 7500. Red-emitting phosphor (ZnS:Se), selected to compliment the system, was dispersed with YAG:Ce throughout PDMS where they were stimulated with a blue LED thereby enabling all desired Kelvin values with differing concentration lenses. Stimulating ZnS:Se with the addition of a UV LED did not provide the ability to change the color value of the set up to the degree required. Many other factors resulted in the decision to remove the UV LED contribution from the multi-Kelvin light source design. The final design incorporated a combination of ZnS:Se and YAG:Ce stimulated with a blue LED to obtain a 2500 Kelvin value. A separate blue LED provides the means to obtain 7500 Kelvin light and the other color values in between, with a linear approximation, by adjusting the amperages of both LEDs. In addition to investigating the feasibility of obtaining the Kelvin values from 2500 to 7500, this thesis also examined the problem of ZnS:Se’s inability to cure in PDMS and a method to create a lens shape to provide equal color values at all points above a phosphor converted LED source. ZnS:Se was found to be curable in PDMS if first coated with a low viscosity silicon oil prior to dispersion within PDMS. The lens configuration consists of phosphors equally distributed in PDMS and cured in the shape of a Gaussian distribution unique to multiple factors in LED-based white light design.

A solar fiber optic lighting system, SP3 from the Swedish company Parans Solar Lighting AB, has been installed in a study area/corridor test site. A collector is tracking the sun during daytime, focusing the direct sun irradiance via Fresnel lenses into optical fibers, which guide the solar light into the building. The illumination properties of the system have been characterized. The energy saving due to reduced need of artificial lighting have been calculated and methods for balancing the artificial lights in the test site have been evaluated. The illumination at the test site using solar light was at least as high as when using the artificial lights and even higher at very clear days. The luminous flux output (500 lm) was somewhat lower than specified by the manufacturer (550 lm) at 100 000 lx direct sun illuminance. The output at 130 000 lx was high 767±33 lm the sunlight coupling efficiency 23 %. However, for a 20 m SP3 system the luminous flux output (400 lm) at 100 000 lx was higher than specified (350 lm). The SP3 system of Parans provides high quality solar light. It has a fuller spectrum close to the spectrum of the sun compared to the fluorescent lights at the test site. The correlated color temperature of the system was 5800±300 K and the color rendering index 84.9±0.5. The lighting energy saved due to decreased need for artificial light was estimated to 19 % in Uppsala which has 1790 annual sun hours. The savings in Italy, which has 3400 sun hours, is 46 %. Additional saving, especially in warmer countries can be obtained due to decreased need for cooling in the building as the solar luminaires provide negligible heat to the indoor air. Economical saving could also be realized by improved well-being of the occupants spending time under the solar luminaires. Three ways of balancing the artificial light due to sunshine fluctuations have been investigated. The global horizontal irradiance could not be used as a control signal for balancing the artificial lights but a pyranometer attached to the SP3 sun tracking collector was usable. Also the signal from an indoor luxmeter sensor could be used for balancing the light. However the signal from the light sensor which makes the SP3 collector to track the sun is probably the most cost effective method as it would serve two purposes; tracking the sun and balancing the artificial lights.

碩士
臺灣大學
電信工程學研究所
98
Correlated color temperature is the temperature of a Planckian radiator which perceived color closely resembles that of a test stimulus. The International Commission on Illumination (CIE) has defined this measurement as being valid under specified viewing conditions and with the test stimulus being of the same brightness as the point of the Planckian radiator. The current method for calculation of the correlated color temperature dates back to 1968 and is based on an obsolete color space which is nowadays not used for any other calculations. The color space is valid for any viewing condition and the brightness is unknown. Color appearance models use viewing conditions and input stimuli to model perceived appearance. Correlates which include brightness and hue are mathematically defined. These parameters are exactly the requirement of the CIE definition for correlated color temperature but are currently not used in the calculation. In this research the definition of color temperature from the Planckian blackbody equation is used to find their locations in color appearance models. Given the blackbody locus as test stimulus different input situations are tested and the models'' outputs are compared. Finally a method for calculating the correlated color temperature in any color appearance model is given which conforms much closer to the CIE definition.

碩士
國立嘉義大學
木質材料與設計學系研究所
107
Light damage of museum object causes material irreversible aging and degradation. It is important to use the proper source of museum lighting. Therefore, evaluating the property of lamps is an indispensable part of conservation work. The main aim of the study presented in the paper was to evaluate museum lighting sources causing color degradation on different materials. Blue wool scale and actual material, including painting and calligraphy paper, mounting materials and Chinese pigments were exposed to four types of white LED lamps with different correlated color temperature and NU-fluorescent lamp. The measurement results provide further information about the benefits of LED lamps for museum lighting. The result of light sources measurement shows that low correlated color temperature (CCT) type LED characterized lower blue wave band ratio and damage factor. Under 300000 lx∙hr of accumulating exposed time, test result revealed LED lamp with low CCT caused a larger Color change of blue wool scale. For painting and calligraphy paper, mounting materials and Chinese pigments, the test result revealed that Color change by NU-fluorescent lamp was greater than LEDs. The comparison of different Color change by LEDs, machine-made paper fading faster under LED with lower CCT. Conversely, hand-made paper, mounting materials, and Chinese pigments fading faster under LED with higher CCT, and the Color change grows as CCT increase. The results of paper P.C. No. (post color number) values change and pH values are similar to the consequence of color change, namely the lamp which caused Color change lager also caused paper P.C. No. values decrease and pH value decrease. Additionally, some sample reacts with certain wavelengths result in larger fading. It is possible that action spectrum of material receiving. The relative evaluations of the discoloration degrees of actual materials after exposed of different light sources revealed LED lamps lower than NU-fluorescent lamp and the degrees decrease as CCT decrease. Furthermore, the LED lamps with lower CCT caused less degaradation. The research verified the blue wave band ratio, damage factor and CCT of light sources as evaluate suitability of light. The LED lamps result lower degradation of materials than NU-fluorescent lamp. It is appropriate to use LED lamp with low CCT as museum lighting.

碩士
國立中央大學
光電科學研究所
100
In this thesis, we study color uniformity of white light LEDs with different package types. Based on the YAG phosphor model, we analyze the angular correlated color temperature deviation (ACCTD) for white light LEDs with different package types and find out which one is lowest. After that, we modify the ACCTD of specific package types with the same correlated color temperature by changing the structure of the package. Finally, we study the ACCTD changes in mid-field region for white light LEDs and define the distance of quasi far-field in color.

碩士
國立臺南藝術大學
博物館學與古物維護研究所
103
Light is a common cause of damage to collections. Paper, textile, binding media , dyes and pigments are particularly sensitive to light. Most of us recognize fading as a form of light damage, but this is only a superficial indication of deterioration that will extends to the physical and chemical structure of collections eventually. Most important, light provides energy to fuel the chemical reactions that produce deterioration. Light damage is cumulative and irreversible. Incandescent lamps have been phased out since 2010 in Taiwan and LED was the latest cutting edge lighting technology, considered as an alternative to traditional light sources. LED waves have swept the museum circle. There are some advantages of LED lighting, such as energy efficiency, ecologically friendly, response fast, small size, low quantity of heat and longer service lifetime. The limit of current technology restricts LED from so-claimed full performance concerning global illumination, color rendering and reliability. Therefore it is necessary to evaluate the use of LED lighting in museums. Blue wool standards were exposed to four types of white LED lamps under different color temperatures. Color changes were measured at each 15,000lx-hr interval twenty times. The accumulated exposed time were 300,000lx-hr. Test results showed that all LED lighting cause fading on blue wool standard grade 1 and the lower color temperature of light the fading rate was faster . The test result is different from former literatures may attributed to commercial LED lamps. The commercial lamps were made by different production and packaging processes based on cost and market trend considerations, such instability will be a potential damage to cultural relics. Color temperature as an indicator of light sources needs more evaluation analysis to testify its performance. It is important to develop a suitable illuminating system light sources in order to put white LED lamps into practical use as a museum light sources.

碩士
國立交通大學
照明與能源光電研究所
105
Recently, white solid-state LECs have attracted intense attention since they exhibit advantages such as low-voltage operation, compatibility with solution processes and employing inert cathode metals. Since different correlated color temperatures (CCTs) of background illumination are necessary for various lighting applications, a real-time tunable CCT of white LECs would be highly desired in modern smart lighting systems. In this work, a widely and dynamically tuning CCT (>10000 K) of white LEC is demonstrated by employing an electrochromic device (ECD) as a real-time controllable color filter. By increasing the applied bias on the ECD to attenuate more the red parts of white EL from the white LEC, the LEC-based white light source becomes more bluish and, in consequence, shows higher CCT. This proposed LEC-based white light source with the characteristics of wide CCT range and real-time tunability is suitable for most lighting applications and modern smart lighting systems.

碩士
國立臺灣科技大學
電子工程系
106
In this thesis, 12 office lighting conditions were designed in terms of 2-level correlated color temperature (CCT) (4000 K, 6000 K), 2-level illuminance (400 lx, 700 lx) and 3-level blue-light peak wavelength (420 nm, 450 nm, 475 nm) using a tuneable LED lighting system. Eye fatigue, sleepiness and task performances of 12 participants were analysed with variables of lighting condition including CCT, illuminance, blue-light peak wavelength, blue-light hazard weighted radiance, and circadian stimulus. These data were analyzed with repeated measure analysis of variance, paired t test, and Pearson product-moment correlation. There are several responses of human beings are significantly influenced by these variables. It indicates that eye fatigue increases more under 6000 K lighting condition compared to 4000 K. It also indicates that eye fatigue increases more under 700 lx lighting condition compared to 400 lx. Paper-based and computer-based task performances under 4000 K lighting condition are better than 6000 K. Therefore, we conclude the 4000 K / 400 lx office lighting is the best one within our designed lighting conditions. Blue-light hazard weighted radiance affects human being more than circadian stimulus and blue-light peak wavelengthes. Higher blue-light hazard weighted radiance is significantly positive correlated to eye fatigue and sleepiness feeling, and is significantly negative correlated to paper-based and computer-based task performance. Therefore, we conclude that choosing a low blue-light hazard weighted radiance office lighting condition would offer a better office environment with improving task performance and reducing eye fatigue and sleepiness feeling.

Dissertação de mestrado em Optometria Avançada
Os sistemas de iluminação que utilizamos nas nossas tarefas diárias são um fator importante para o desempenho visual. Estes sistemas devem ser adequados às necessidades visuais exigidas por este tipo de tarefa. O objetivo deste estudo foi analisar a influência de determinados parâmetros da iluminação, nomeadamente a iluminância, cor e temperatura de cor, nos parâmetros acomodativos oculares. Foram avaliados 26 sujeitos com idades compreendidas entre os 18 e os 35 anos, sem problemas acomodativos e com visão das cores normal. Primeiro, determinou-se o erro refrativo, os parâmetros acomodativos e de visão binocular de todos os participantes. De seguida, os parâmetros acomodativos foram determinados em diferentes condições de iluminação. Foi medida a amplitude de acomodação e flexibilidade acomodativa em diferentes níveis de iluminância (30lx, 150lx e 400lx), iluminação colorida (verde e vermelho) e em iluminações com diferentes temperaturas de cor correlacionada (2500 K e 4500 K) que procuravam mimetizar condições de luz do dia para temperaturas de cor correspondentes. Para a realização das medidas sob diferentes condições foi utilizada a lâmpada Ledigma (Ledigma Ltd, Vilnius, Lithuania). Na variação da iluminância, verificou-se um aumento estatisticamente significativo na amplitude de acomodação dos 30lx para os 150lx (p<0,001; t-student test). A amplitude de acomodação medida com a iluminância de 400lx também apresentou um aumento estatisticamente significativo (p<0,001; t-student test) quando comparado à obtida com iluminância de 30lx. Contudo a amplitude de acomodação medida com a iluminância de 150lx não apresentou diferenças estatisticamente significativas quando compara à obtida com a iluminância de 400lx (p>0,05). Em termos de flexibilidade acomodativa, esta apresentou um aumento estatisticamente significativo dos 30lx para os 400lx (p<0,001; t-student test). Relativamente à iluminação colorida, os valores de amplitude de acomodação apresentaram uma diminuição estatisticamente significativa com a iluminação vermelha, quando confrontados com os obtidos com a luz branca (p=0,016; t-student test). A amplitude de acomodação medida sob a iluminação vermelha, apresentou uma diminuição estatisticamente significativa quando comparada com a obtida com a cor verde (p<0,001; t-student test). No entanto, a amplitude de acomodação medida com a luz de cor verde não apresentou diferenças estatisticamente significativas quando comparada à obtida com a luz branca (p>0,05). Em termos de flexibilidade acomodativa, não foram encontrados valores estatisticamente significativos (p>0,05; t-student test) para as condições testadas. O mesmo aconteceu com a temperatura de cor, em que não foram encontrados valores estatisticamente significativos entre os 2500 K e os 4500 K (p>0,05; t-student test). Os resultados encontrados sugerem uma associação entre alguns parâmetros acomodativos e condições de iluminação específica. Iluminação imprópria ou com parâmetros desajustados podem causar uma variação nos parâmetros acomodativos e gerar sintomatologia.
The lighting systems that is used in our daily tasks are an important factor in our vision performance. These systems must be suitable to the visual needs required by these types of tasks. The aim of this work was to evaluate the influence of specific lighting parameters, in particular illuminance, color and color temperature, on ocular accommodative parameters. Twenty-six subjects were accessed with ages between 18 and 35 years, without accommodative disorders and with normal vision color. First, refractive error, accommodative parameters and binocular vision of all the participants were measured. Then, the accommodative parameters were determined in different illumination conditions. The amplitude of accommodation and accommodative facility were measured under different illuminance levels (30lx, 150lx and 400lx), colored lighting (green and red) and under different correlated color temperature (2500K and 4500K) that trying to imitate daylight conditions for corresponding color temperatures. Measurements under the different conditions were done using a Ledigma luminary (Ledigma Ltd, Vilnius, Lithuania). Considering the illuminance, there was a statistically significant increase in the amplitude of accommodation from 30lx to 150lx (p<0.001; t-student test). The amplitude of accommodation measured with 400lx illuminance also showed a statistically significant increase (p<0.001; tstudent test) when compared to that obtained with 30lx illuminance. However, the amplitude of accommodation measured with the illuminance of 150lx didn’t present statistically significant differences when compared to that obtained with the illuminance of 400lx (p>0.05). In terms of accommodative flexibility, this increased significantly from 30lx to 400lx (p<0.001; t-student test). Regarding the colored lighting, the accommodation amplitude values presented significantly lower values with red lighting when compared with those obtained with white light (p=0.016; t-student test). Accommodation amplitude measured under red illumination, showed a statistically significant decrease when compared to that obtained with the green color (p<0.001; tstudent test). However, the amplitude of accommodation measured with green light did not present statistically significant differences when compared to that obtained with white light (p>0.05). In terms of accommodative flexibility, no statistically significant values were found for the conditions tested (p>0.05; t-student test). The same happened to the color temperature, where no statistically significant values were found between 2500K and 4500K (p>0.05; t-student test). Results seemed to show that particular light conditions influenced the amplitude of accommodation and accommodative facility. Improper lighting or inadequate parameters can cause a variation in accommodative parameters and cause symptomatology.
Este trabalho foi financiado por Fundos Nacionais através da FCT – Fundação para a Ciência e a Tecnologia no âmbito do projeto PTDC/FIS-OTI/31486/2017

碩士
國立中央大學
光電科學研究所
100
The different correlated color temperatures of lamps are used in different places. The warm color of lamps is often used in street lighting on the way home. Boiler rooms and steelworks often use cold colors of lamps to increase the sense of cool. But are the visual comfort and fatigue affected by different correlated color temperatures ? This study aims to investigate the discomfort glare effects of traditional fluorescent tubes with different correlated color temperature and illuminance. By utilizing the evaluation platform and the experimental procedure previously established in the research group, psychophysical experiments were performed to obtain subjective ratings of visual comfort through questionnaires and objective scores on visual fatigue from the critical flicker fusion (CFF) measurements. Detailed experimental design and lighting uniformity measurements were accomplished. Parameters in the DIALux simulation were adjusted according to the experimental design and uniformity measurements; simulation results were used to set the experimental illuminance levels. Statistical analyses of the experimental data were conducted in SPSS to compare visual comfort, visual fatigue and task performance under different lighting conditions. The only significant effect was the surrounding illuminance on the CFF values. Posteriori comparisons showed that the illuminance level of 1000 lux is better than 500 lux in the aspect of objective visual fatigue characteristized by the CFF values. The experimental results showed that changing correlated color temperature did not affect human visual performance in the aspects considered in this study.

碩士
國立交通大學
光電工程研究所
101
Recently, the white LEDs (WLEDs) burgeons due to the advantages of small sizes、high efficiency and power saving. To fully substitute the traditional lighting and bring human beings the comprehensive applications, enhancement of luminous efficiency and the improvement of color uniformity have become important issues. WLEDs composed of the blue LED chips and yellow phosphor are most common to use in industry area, among which the traditional dispensing method possess the characteristics of easy packaging and low cost, so this method is adopted universally. In spite of various advantages of tradition dispensing method, structure for this kind of WLEDs still have some problems such as imhomogeneous angular-dependent correlated-color temperature (CCT) , thus the serious yellow-ring phenomenon was unavoidable. To solve this problem, we proposed the utilization of nano-particles to ameliorate the non-uniformity of CCT and further improve the luminous efficiency. In this thesis, the the ZrO2 nano-particle was employed to co-doped with phosphor and silicone encapsulant because of thermal stable、wear-resisting and low cost, via the high scattering effect of nano-particles, blue light emitted from chip was altered significantly, and the angular-dependent CCT uniformity was improved, besides, this structure also provides higher lumen output. Finally, we demonstrate that Mie-scattering dominates the whole scattering process by the analysis of optical simulation software, the capability of scattering was increased with less than 1% ZrO2 usage of nano-particles, hence we can spare the redundant usage of phosphor and make a cost reduction in WLEDs fabrication by doping ZrO2 nano-particles. .

碩士
國立雲林科技大學
電子工程系
103
This thesis is divided into two parts,(1) Discussing 4 kinds of LED street lights in different levels fog conditions, they are RGBY-mixed LEDs white-light with high color temperature, RGBY-mixed LEDs white-light with color temperature, Phosphors-activative LEDs white-light with high color temperature and Phosphors-activative LEDs white-light with low color temperature. The use of qusetionnaires to identify 4 kinds of lights on human visual selection more clear and comfortable in fog；(2)When people are in the reading situation,using a commercially available CNS Philips light bulb with high color temperature and low color temperature. With EEG、ECG between all the experiment. Study (A)：Subjects were healthy for 27 Students and graduate students, each one of the subjects were all watching the experiment after pictures, and subjective ratings were due to the questionnaire, the results of the analysis show a low color temperature LED under foggy conditions, visual effects better than the high color temperature LED. Phosphors-activative LEDs is better than RGBY-mixed LED in heaviest fog Study (B)：26 healthy students and graduate students were participated in this experiment, each subject accepted two groups of light illuminance：the CNS high color temperature LED bulb and the CNS low color temperature LED bulb. A questionnaire was finished in which each one requested to show their subjective feeling after the experiment. EEG、ECG singals were recorded between all experiment and measuring eye strain after resting and reading.

碩士
崑山科技大學
電子工程研究所
102
Recently, the white LEDs burgeons due to the advantages of small sizes、high luminous efficiency and power saving. To fully substitute the traditional lighting and bring human beings the comprehensive applications, enhancement of luminous efficiency and the improvement of color uniformity have become important issues. In the case that LED light source gradually replaces traditional light source, the color temperature is arousing attention from industry. We can explore the relationships between color temperature and comfort range by analyzing the color temperature in physiological and psychological attributes. Then, apply it to different circumstances and purposes. We can see lots of LED applications for color of lighting today. In this paper, we have investigated the increase of the light extraction efficiency and improvement of the color temperature uniformity per view angle of a white light-emitting diode by utilizing ZrO2 / HfO2 hybrid nanoparticles. The white LEDs with a correlated color temperature (CCT) of 6060 K, 5.05 wt％ phosphor is used without ZrO2 / HfO2 hybrid particles doping, whereas 3.53 wt％ phosphor is used after adding 1.0 wt％ ZrO2 / HfO2 hybrid particles,with the same CCT, the luminous flux is increased by 0.67％, with the ZrO2 / HfO2 hybrid particles doping, and the CCT deviation is also improved from 1216 K to 316 K. Simultaneously, the amount of phosphor is reduced 30.1％ with the ZrO2 / HfO2 hybrid particles doping. The results showed that all the ZrO2 / HfO2 hybrid particles have higher luminous flux than the without doping ZrO2 / HfO2 hybrid particles, the without doping ZrO2 / HfO2 hybrid particles, the luminous flux increased to a plateau value of 141.8 lm as the ZrO2 / HfO2 content in the hybrid material was increased to 0.3 wt％, compared to the LED without ZrO2 / HfO2 doping hybrid particles, the luminous flux of the LEDs with ZrO2 / HfO2 doping hybrid particles was increased by 5.82％ at 350 mA.