Study objectives Blue-depleted lighting reduces the disruptive effects of evening artificial light on the circadian system in laboratory experiments, but this has not yet been shown in naturalistic settings. The aim of the current study was to test the effects of residing in an evening blue-depleted light environment (LE) on melatonin levels, sleep, neurocognitive arousal, sleepiness and potential side-effects. Methods The study was undertaken in a new psychiatric hospital unit where dynamic light sources were installed. All light sources in all rooms were blue-depleted in one half of the unit between 1830h and 0700h (melanopic lux range: 7 – 21, melanopic equivalent daylight illuminance range (M-EDI): 6-19, photopic lux range: 55-124), whereas the other had standard lighting (melanopic lux range: 30-70, M-EDI range: 27-63, photopic lux range: 64-136), but was otherwise identical. Twelve healthy adults resided for five days in each light LE in a randomized cross-over trial. Results Melatonin levels were less suppressed in the blue-depleted LE (15%) compared with the normal LE (45%) (p=0.011). DLMO was phase advanced more (1:20h) after residing in the blue-depleted LE than after the normal LE (0:46h) (p=0.008). Total sleep time was 8.1 minutes longer (p=0.032), REM sleep 13.9 minutes longer (p<0.001), and neurocognitive arousal was lower (p=0.042) in the blue-depleted LE. There were no significant differences in subjective sleepiness (p=0.16) or side-effects (p=0.09). Conclusion It is possible to create an evening light environment that has an impact on the circadian system and sleep without serious side-effects. This demonstrates the feasibility and potential benefits of designing buildings or hospital units according to chronobiological principles and provide a basis for studies in both non-clinical and clinical populations.