Study Of Visual Evaluation Methodology And Technology For Comfort Under LED Interior Illumination

In recent years, LED (light emitting diode) has been rapidly utilized in the field of indoor lighting, which makes the research on visual comfort under LED interior illumination become a hot topic. In order to reach the demands of visual tasks for human being, there have been many standards to specify the illuminance, correlated color temperature (CCT) and chromaticity coordinates for various lighting sources. These present methods are simple and practicable but not suitable for evaluating the visual comfort under LED illumination. So far, there is no effective and feasible method to assess the comfort of lighting comprehensively and systematically. Hence, this study focuses on establishing a systematic evaluation method for comfort along with the key techniques based on the application of LED in indoor lighting.To ensure the completeness of this dissertation and the validity of the experimental data, an overall research scheme was firstly designed and then a series of measurements were implemented to test the related instruments employed in this study. Based on the expected target of this dissertation, the entire research was divided into three main parts, i.e. the study and modeling of lighting comfort based on the CCT and illuminance, the study and modeling of lighting comfort based on the chromaticity coordinates, and the verification for the two models of lighting comfort as well as the establishment of the overall evaluation technology for lighting comfort.The study of lighting comfort based on the CCT and illuminance focuses on the effects of the CCT and illuminance on the visual comfort for interior lighting. A total of 12 CCT levels ranged from 2000 K to 100000 K was adopted in this experiment to ensure an enough coverage with the extreme cases being investigated, since the CCT in daily applications of life and work generally ranged from 2700 K to 7000 K. Meanwhile, three levels of illuminance, including 350 lx,500 lx, and 1000 lx, were employed in this experiment. Based on the visual data, the influence significances of the CCT and illuminance on the lighting comfort were discussed by means of multi-factor analysis of variance, which indicates that the CCT, rather than illuminance, is the significant factor to impact the lighting comfort under the conditions of this experiment. Therefrom, a model was built using Gaussian function to characterize the effect of CCT on the lighting comfort. Furthermore, the illuminance was introduced into this model on the basis of the effect of illuminance on the comfort, so that the modeling of lighting comfort was finally achieved as the function of CCT and illuminance, of which the validity was verified by the confirmatory experiment.The study of lighting comfort based on the chromaticity coordinates aims to analyze the characteristics of lighting comfort for individual specific indoor scenes. The different LED lighting environments, with 46 groups of chromaticity coordinates distributed along 7 isotemperature lines, were tested to explore their effects and patterns on the comfort, white sensation as well as the 7 emotional responses of color light for the indoor lighting scenarios of office, dining room, living room, leisure facility, bedroom and toilet. The 7 isotemperature lines are with the CCT of 2500 K,2856 K,4000 K,5000 K,6500 K,9300 K and 15000 K, respectively, and the 7 emotional responses are dark-light, cool-warm, classical-modern, passive-active, relaxed-tense, feminine-masculine and elegant-vulgar. Herewith, the subjective data on comfort and relevant evaluations from the psychophysical experiment were collected, and the raw data of category names assigned by all the observers were converted to the equal-interval scale values by using Case V of Thurstone’s law on comparative judgment. And then, the Pearson correlation analysis and factor analysis were implemented to investigate the relationships between the comfort and white sensation as well as the 7 emotional responses for different lighting scenes, which concluded that the lighting comfort was impacted by the two aspects of light for meeting the needs of human visual performance and inducing the human emotions. Thus, a multiple linear regression model of lighting comfort was established by the white sensation and 7 emotional responses. Furthermore, the mathematical links were set up between the chromaticity coordinates of lighting and the white sensation as well as the emotional responses via polynomial fitting. Hence, the model of lighting comfort based on the chromaticity coordinates was built through the bridge of white sensation or 7 emotional responses, which could be applied to the comfort evaluation for specific indoor lighting scenes.A reading experiment and an immersion experiment under LED lighting were designed respectively to test the proposed evaluation models of lighting comfort. In the reading experiment, a 2-hour numerical verification task without rest in the whole procedure was implemented to collect the data of visual fatigue and visual performance. And the analysis of the relationships between the two indices and lighting comfort demonstrates the validity and feasibility of the proposed method. In the immersion experiment,12 test illumination conditions were adopted to estimate the lighting comfort, which were further used to verify the two developed comfort models respectively. On this basis, an implementation scheme was established for visual comfort evaluation under LED indoor illumination by the combination of the two lighting comfort models proposed in this study.Finally, the main research contents and results of this paper were summarized, and the perspectives of the future study were also forecasted.