Neural Regeneration Research ›› 2022, Vol. 17 ›› Issue (9): 1929-1936.doi: 10.4103/1673-5374.335141

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Alerting effects of light in healthy individuals: a systematic review and meta-analysis#br#

Yi-Man Mu1, 2, Xiao-Dan Huang3, Sui Zhu1, 2, Zheng-Fang Hu3, Kwok-Fai So3, 4, 5, 6, 7, Chao-Ran Ren3, 4, 5, 6, 7, Qian Tao1, 2, 5, 6, *   

  1. 1Department of Public Health and Preventive Medicine, School of Basic Medicine, Jinan University, Guangzhou, Guangdong Province, China; 2Division of Medical Psychology and Behavior Science, School of Basic Medicine, Jinan University, Guangzhou, Guangdong Province, China; 3Guangdong-Hongkong-Macau Institute of CNS Regeneration, Ministry of Education CNS Regeneration Collaborative Joint Laboratory, Jinan University, Guangzhou, Guangdong Province, China; 
    4Guangzhou Regenerative Medicine and Health Guangdong Laboratory, Guangzhou, Guangdong Province, China; 5Center for Brain Science and Brain-Inspired Intelligence, Guangdong-Hong Kong-Macao Greater Bay Area, Guangzhou, Guangdong Province, China; 6Neuroscience and Neurorehabilitation Institute, University of Health and Rehabilitation Science, Qingdao, Shandong Province, China; 7Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu Province, China
  • Online:2022-09-15 Published:2022-03-05
  • Contact: Qian Tao, MD, taoqian16@jnu.edu.cn.
  • Supported by:
    This work was supported by the National Natural Science Foundation of China, No. 82172530 (to QT); Science and Technology Program of Guangdong, No. 2018B030334001 (to CRR); Guangzhou Science and Technology Project, No. 202007030012 (to QT).

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Abstract: Light plays an essential role in psychobiological and psychophysiological processes, such as alertness. The alerting effect is influenced by light characteristics and the timing of interventions. This meta-analysis is the first to systematically review the effect of light intervention on alertness and to discuss the optimal protocol for light intervention. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020181485), we conducted a systematic search of the Web of Science, PubMed, and PsycINFO databases for studies published in English prior to August 2021. The outcomes included both subjective and objective alertness. Subgroup analyses considered a variety of factors, such as wavelength, correlated color temperature (CCT), light illuminance, and timing of interventions (daytime, night-time, or all day). Twenty-seven crossover studies and two parallel-group studies were included in this meta-analysis, with a total of 1210 healthy participants (636 (52%) male, mean age 25.62 years). The results revealed that light intervention had a positive effect on both subjective alertness (standardized mean difference (SMD) = –0.28, 95% confidence interval (CI): –0.49 to  –0.06, P = 0.01) and objective alertness in healthy subjects (SMD = –0.34, 95% CI: –0.68 to –0.01, P = 0.04). The subgroup analysis revealed that cold light was better than warm light in improving subjective alertness (SMD = –0.37, 95% CI: –0.65 to –0.10, P = 0.007, I2 = 26%) and objective alertness (SMD = –0.36, 95% CI: –0.66 to  –0.07, P = 0.02, I2 = 0). Both daytime (SMD = –0.22, 95% CI: –0.37 to  –0.07, P = 0.005, I2 = 74%) and night-time (SMD = –0.32, 95% CI: –0.61 to –0.02, P = 0.04, I2 = 0) light exposure improved subjective alertness. The results of this meta-analysis and systematic review indicate that light exposure is associated with significant improvement in subjective and objective alertness. In addition, light exposure with a higher CCT was more effective in improving alertness than light exposure with a lower CCT. Our results also suggest that both daytime and night-time light exposure can improve subjective alertness.

Key words: correlated color temperature, illuminance, light, meta-analysis, objective alertness, subjective alertness, time of light intervention, wavelength