In this thesis, we have successfully accomplished a GUI platform for multi-color LED mixing calculation. The simulation result is well verified by a LED matrix with tunable CCT value and high CRI value. Although the crosstalk is occurred by the control circuit, the platform still can modify the simulation result and expect the synchronized mixing SPD. Thus, this GUI platform will be a powerful tool for the further LED lighting study.
In the future, the program is able to expand or replace some new elements. For example, the new generation light source qualification factor, color quality scale (CQS), which is developed by Yoshi Ohno and Wendy Davis at national institute of standard and technology (NIST), USA [19]. This factor is established to modify the CRI value in order to achieve better correlations between the human feeling and the evaluating scores.
CQS pronounced 15 high saturation color chips to replace the 8 low saturation samples used in CRI [Fig. 5.1]. The samples are selected to span around the entire hue circle and are expected to have better representation of the practical object colors.
Besides, the more uniform and advanced color space, CIE 1976 L*a*b* is adopted than the original 1964 W*U*V* color space. Current research shows that only decrease in chroma will have negative effects. Thus, CQS also takes this into consideration, and maintain the evaluating score when the chroma is increased. This is different than the CRI evaluation, which will decrease the score for any color deviation. Furthermore, CQS takes root-mean-square (RMS) than the traditional arithmetic mean to evaluate the overall score. This is used to emphasize the performance of each sample.
65
Fig. 5.1 Color chips used in CQS
However, some parts of this new scale are under developing, such as new human adaptation model. Besides, the practical human experiment results are not published, and the CIE still not accepts it as the global standard. Therefore, we still took the CRI into our consideration until the accurate calculating process is available.
Besides the modification of the GUI platform, some LED lighting issues can also be discussed in the future. Some research had done to discuss the impact of the working performance under different lighting intensity. Beutell is the first one who attempted to announce a model for specifying the necessary illuminance for different task [6]. And the idea was exploited by Weston who developed it into one of the most widely used methods of investigating the effects of lighting and work [6]. Weston devised a very simple task which was largely visual and in which the critical detail was easy to identify and measure. The task is well known as the Landolt ring chart [Fig. 5.2]. Thus, the tester can analysis the experimental scores to evaluate the lighting performance.
Fig. 5.2 Landolt ring chart
66
However, only luminance issue is considered in the past experiment. Nowadays, the LED produces a chance to receive many different spectrums with the same chromaticity. This phenomenon is called the metameric spectrum in color science. As the previous studies had done on the working performance with different lighting intensity, we are more interesting in the influence of the metameric spectrum to the working performance, or the color contrast to the working performance. Although the parameters, such as CRI value or CQS, can describe the color performance of the light source, they have no link between these index values and the human working performance. Thus, our GUI platform can be used to produce different SPD light sources with the same CCT value, and then two environments that fulfilled the traditional lighting requirements with different SPDs can be constructed. Then, we can compare the working performance under the different spectrum condition and find out more LED lighting properties.
67
Reference
[1] “Global Optoelectronics Industry Market Report and Forecast“, OIDA, 2007 [2] Daniel A. Steigerwald, Jerome C. Bhat, Dave Collins, Robert M. Fletcher, Mari
Ochiai Holcomb, Michael J. Ludowise, Paul S. Martin, Serge L. Rudaz,
“Illumination With Solid State Lighting Technology,” IEEE Journal On Selected Topic in Quantum Electronics, Vol. 8, No. 2, pp.310-320, 2002.
[3] Advanced Lighting Guidelines Project Team, “Advanced Lighting Guidelines,”
New Buildings Institute, Inc, 2003.
[4] “Lighting Applications Guideline for LEDs,” Lighting Research Center, Rensselaer Polytechnic Institute, 2002.
[5] http://www.philipslumileds.com/technology/lumenmaintenance.cfm
[6] P. R. Boyce ,“Human Factors in Lighting”, Applied Science Publishers Ltd, England, 1981.
[7] Jennifer A. Veitch, Guy R. Newsham, “Determinants of Lighting Quality I: State of the Science”, Journal of the Illuminating Engineering Society, Winter, pp.
92-106, 1998.
[8] Jennifer A. Veitch, “Determinants of Lighting Quality II: Research and
Recommendations”, Lighting Research & Recommendations, National Research Council of Canada, 1996.
[9] Neil Holger White Eklund, “Multiobjective Visible Spectrum Optimization: A Genetic Algorithm Approach”, Ph. D Thesis, Rensselaer Polytechnic Institute, 2002.
68
[10] A. Zukauskas, R. Vaicekauskas, F. Ivanauskas, R. Gaska, M. S. Shur,
“Optimization of White Polychromatic Semiconductor Lamps”, Applied Physics Letters, Vol. 80, pp. 234-236, 2002.
[11] R. Gaska, A. Zukauskas, M. S. Shur, M. Asif Khan, “Progress in III-Nitride Based White Light Sources”, Solid State Lighting II, Proc. SPIE, Vol. 4776, pp.82-96, 2002.
[12] A. Zukauskas, R. Vaicekauskas, F. Ivanauskas, H. Vaitkevicius, M. S. Shur,
“Spectral Optimization of Phosphor-conversion Light-emitting Diodes for Ultimate Color Rendering”, Applied Physics Letters, Vol. 93, 05115, 2008.
[13] A. Zukauskas, R. Vaicekauskas, F. Ivanauskas, H. Vaitkevicius, M. S. Shur,
“Rendering a Color Palette by Light-emitting Diodes”, Applied Physics Letters, Vol. 93, 021109, 2008.
[14] Noboru Ohta, Alan R. Robertson, “Colorimetry,” John Wiley & Sons Ltd, England, 2005.
[15] Commission Internationale de l’Éclairage: Method of measuring and specifying colour rendering properties of light sources. CIE Central Bureau CIE 13.2-1974.
[16] “Lighting Applications Guideline for LEDs”, Lighting Research Center, Rensselaer Polytechnic Institute, 2002.
[17] Yoshi Ohno, “Color Rendering and Luminous Efficacy of White LED Spectra”, Fourth International Conference on Solid State Lighting, Proc. SPIE, Vol. 5530,
pp. 88-98, 2004.
[18] B. Ackermann, V. Schulz, C. Martiny, A. Hilgers, X. Zhu, “Control of LEDs”, Industry Applications Conference, Conference Record of the 2006 IEEE, Vol. 5,
pp. 2608-2615, 2006.
[19] Wendy Davis, Yoshi Ohno, “Development of a Color Quality Scale”, National Institute of Standards and Technology, 2006.