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Roadway lighting Research


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Research & Development

Roadway lighting Research on Color of Light Preference for Thai's. These research objectives are to find the suitable luminance for the user's vision, to find the suitable color temperature for driving, and to study the driver's preferences. Bureau of Road Research and Development initiated this investigation that has been conducted by Chulalongkorn University, King Mongkut's Unversity of Technology, Bioarchitek Co.Ltd. and InfraPlus Co.Ltd. Custom software has been created to effectively control CCT and light levels for different scene settings, as well as to capture observers' location by global positioning system (GPS) indicating their visual performance where they were asked to read a little on sidewalk correctly. LMK CCD camera with its software for photo imaging technique has been used to measure and evaluate uniformity and brightness of the road. The utilization of an imaging luminance photometer instead of a conventional spot meter eases the luminance measurements and gives many new possibilities in analyzing the luminance distributions. This significantly reduced time in luminance measurement with more accurate results. EN 13201-2 standards. The LED pole was custom design to be able to hold 3 sets of CCT LEDs: 3000 K, 4000 K, and 5700 K with smart control for 3 sets of light levels providing 100% same brightness as that provided by HPS, 75% and 50%. Total varying 3 sets of CCTs with 3 sets of light levels was 9 settings. Forty subjects, aging between 20 - 59 years old with normal color vision completed the experiments. An online questionnaire was filled by each object after finishing each experiment set to evaluate their visual comfort and preferences. There was a screening process to eliminate unusual and unreliable data before analysis using ANOVA and Chi-Square. Results showed that at the same road brightness, all CCT LEDs at 100% outperformed HPS in terms of both visual performances, visual preference and visual comfort. The reason could be because of the Color Rendering Index (CRI) of LEDs that is higher than HPS. Visual performance in term of visibility indicated that when LED was on 75%, visibility distance was similar to that of HPS when on at 100%. However different CCTs did not have a significant correlation with visibility distance. Results from visual preference explained that LED 4000 K at 100% brightness was preferred by the majority, followed by 5700 K and 3000 K, respectively. For visual comfort, most people preferred LED 4000 K at 75% brightness. As a consequence, results could be used to apply for a new standard for highways in Thailand to use different CCT at different context.

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