Browsing by Subject "Color temperature"

Now showing 1 - 4 of 4

Open Access
Color science and technology of novel nanophosphors for high-efficiency high-quality LEDs
(2011) Erdem, Talha
Today almost one-fifth of the world‟s electrical energy is consumed for artificial lighting. To revolutionize general lighting to reduce its energy consumption, high-efficiency, high-quality light-emitting diodes (LEDs) are necessary. However, to achieve the targeted energy efficiency, present technologies have important drawbacks. For example, phosphor-based LEDs suffer from the emission tail of red phosphors towards longer wavelengths. This deep-red emission decreases substantially the luminous efficiency of optical radiation. Additionally, the emission spectrum of phosphor powders cannot be controlled properly for high-quality lighting, as this requires careful spectral tuning. At this point, new nanophosphors made of colloidal quantum dots and crosslinkable conjugated polymer nanoparticles have risen among the most promising alternative color convertors because they allow for an excellent capability of spectral tuning. In this thesis, we propose and present high-efficiency, highquality white LEDs using quantum dot nanophosphors that that exhibit luminous efficacy of optical radiation ≥380 lm/Wopt, color rendering index ≥90 and correlated color temperature ≤4000 K. We find that Stoke‟s shift causes a fundamental loss >15%, which limits the maximum feasible luminous efficiency to 326.6 lm/Welect. Considering a state-of-the-art blue LED (with 81.3% photon conversion efficiency), this corresponds to 265.5 lm/Welect. To achieve 100 and 200 lm/Welect, the layered quantum dot films are required to have respective quantum efficiencies of 39 and 79%. In addition, we report our numerical modeling and experimental demonstrations of the quantum dot integrated LEDs for the different vision regimes of human eye. Finally, we present LEDs based on the color tuning capability of conjugated polymer nanoparticles for the first time. Considering the outcomes of this thesis, we believe that our research efforts will help the development and industrialization of white light emitting diodes using nanophosphor components.
Open Access
A comparative study on spatial perception in real and virtual office environments under different lighting conditions
(2019-01) Kuş, Büşra
The aim of study iş to conduct a comparison between real and virtual environments from the spatial point of view under different lighting conditions. In this study, visually same office environments were created in real environment (RE) as well as in virtual environments (VE) in order to be able to observe only the perception between the two environments. The experiment was conducted in full-scale office environment and virtual environment by using Unity 3D program with participating of sixty people. These environments were appraised under 4000K (cool white light) and 6500K (daylight) lighting color temperatures. An office room in Bilkent University and Environmental Design building was used to carry out the experiments. The participants were asked to experience the environments firstly, later on they were as requested to answer the previously prepared questionnaire with semantic differential scale. As a result of this study one can say that the perceptions of both environments RE and VE were similar to some extend in more than half of the 12 adjective pairs under both color temperature. Adjectives such as usual-unusual, dynamic-static, spacious-confined and harmonious-discord demonstrated significant differences for both environments. Moreover, participants perceived real environment more spacious, usual, harmonious and less dynamic than virtual environment under both lighting conditions. Only the functional-nonfunctional and formal-informal adjective pairs behaved significantly different under 4000K and 6500K respectively. There were no significant effects of color temperatures in real and virtual environments.
Open Access
Effects of color temperature on projected fractal light patterns: visual interest and emotional response
(2020-07) Sezer, Buse
The aim of the present study is to examine the effects of color temperature of projected fractal patterns on visual interest and emotional response in interior spaces. The experiment consisted of two phases, which were carried out with two independent participant groups. In the first phase, the effects of five different complexity levels of two dimensional fractal patterns (D = 1.1, D = 1.3, D = 1.5, D = 1.7, D = 1.9) on visual interest and emotional response were examined. In the second phase, the effects of three different natural light color temperatures (noon sky – 4000K, overcast sky – 6500K, clear sky – 12000K) of three dimensional projected fractal patterns on visual interest and emotional response in interior spaces were evaluated. The participants consisted of sixty undergraduate and graduate students enrolled in İhsan Doğramacı Bilkent University. Results demonstrated that, in the first phase, the most visually interesting fractal pattern was high-complexity D = 1.7. Moreover, the results indicated that the complexity level of fractal patterns had no significant influence on participants’ pleasure state, whereas complexity level had positive significant effects on participants’ arousal state. In the second phase, results indicated that the most visually interesting projected fractal pattern was high complexity D = 1.7 for all color temperatures (4000K, 6500K, & 12000K). Therefore, color temperature had no significant influence on the choice of fractal pattern complexity level in terms of visual interest. Regarding emotional response, the findings also demonstrated that color temperature had no significant influence on pleasure and arousal state. Consequently, the most influential outcome of the study was that, compared with color temperature, complexity level is a more significant factor related to visual interest and emotional response. The findings of the present study guides designers on the implementation of natural light patterns to for visual interesting interior spaces.
Open Access
Metrics for light source design
(Springer, 2019-01) Erdem, Talha; Demir, Hilmi Volkan; Erdem, Talha; Demir, Hilmi Volkan
In this part of this brief, we summarize the metrics that need to be considered for designing light sources. We start with metrics on the shade of color and then continue with color rendering and photometry.