Sleep deprivation is common among intensive care patients and may be associated with delirium. We investigated whether the implementation of a bundle of non-pharmacological interventions, consisting of environmental noise and light reduction designed to reduce disturbing patients during the night, was associated with improved sleep and a reduced incidence of delirium. The study was divided into two parts, before and after changing our practice. One hundred and sixty-seven and 171 patients were screened for delirium pre- and post-intervention, respectively. Compliance with the interventions was > 90%. The bundle of interventions led to an increased mean (SD) sleep efficiency index (60.8 (3.5) before vs 75.9 (2.2) after, p = 0.031); reduced mean sound (68.8 (4.2) dB before vs 61.8 (9.1) dB after, p = 0.002) and light levels (594 (88.2) lux before vs 301 (53.5) lux after, p = 0.003); and reduced number of awakenings caused by care activities overnight (11.0 (1.1) before vs 9.0 (1.2) after, p = 0.003). In addition, the introduction of the care bundle led to a reduced incidence of delirium (55/167 (33%) before vs 24/171 (14%) after, p < 0.001), and less time spent in delirium (3.4 (1.4) days before vs 1.2 (0.9) days after, p = 0.021). Increases in sleep efficiency index were associated with a lower odds ratio of developing delirium (OR 0.90, 95% CI 0.84–0.97). The introduction of an environmental noise and light reduction programme as a bundle of non-pharmacological interventions in the intensive care unit was effective in reducing sleep deprivation and delirium, and we propose a similar programme should be implemented more widely.