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. 2019 May 17;9:7560. doi: 10.1038/s41598-019-43864-6

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© The Author(s) 2019

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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The biological effect on human’s eyes before and after irradiation by artificial lights (1900 K, 3000 K, 4000 K and 6600 K), the experiment was repeated by three times at different time. (a) The first non-invasive tear break-up time. (b) The average non-invasive tear break-up time. (c) The tear meniscus height. (d) The red eye analysis (B grading). (e) The red eye analysis (L grading).