Abstract: The aim of this paper is to identify the effect of night light on delirium occurrence in post-operative cardiac patients. Design: A randomized prospective observational study.Method. 60 patients (25 in the experimental group, 35 in routine group) who underwent cardiac surgery from 1/ May 2016 to 30 / December 2016 and met inclusion criteria were enrolled. The patients were sorted randomly to sleep with or without eye masks during the first three nights. The Chinese version of Richards-Campbell Sleep Questionnaire (ROCK) was used to evaluate the subjective sleep quality. The NEECHAM Confusion Scale was used to assess delirium each morning for each patient. Result: Total Mean ± SD of the overall score of ROCK items in the three nights was 49.05 ± 5.65 in routine group versus 58.73 ± 5.06 in the experimental group (P value <0.001). Total Mean ± SD of the overall score of the NEECHAM in the three nights was 20.90 ± 1.82 in routine care group versus 23.66 ± 1.613in experimental group. A dramatic decrease in delirium occurrence in the experimental group versus routine group (P value <0.001).Conclusion: This non-pharmacological nursing intervention as eye mask is efficient for decreasing delirium in the critically ill patient.