Testing the effects of residing in an evening blue-depleted hospital light environment

INTERVENTION: This study examines the benefits and risks of residing in an environment with blue depleted lighting compared to residing in an environment with normal lighting. The trialists will recruit adult volunteers to reside in a newly built 40‐bedded acute psychiatric unit (prior to the unit opening for patient admissions). Twenty beds are located in a hospital ward with normal lighting conditions that has 3000K (Kelvins) color temperature (which is the same as found in other hospital wards and many homes). The other 20 beds are located in a ward that has tunable light emitting diode (LED) sources and provides blue‐blocking filters in front of all the windows in the evening. The layout, facilities and light intensity (photopic lux) are the same in both wards, but individuals are exposed to a different spectrum of light in each ward. 1. Normal indoor light (control condition): The 20 patient rooms, their corresponding bathrooms and all common areas in the ward have ordinary indoor lighting installed (Glamox, Norway). The light intensity is dimmed to 20% (of the maximum) during the night (from 23:00 to 07:00). 2. Blue‐depleted light (experimental condition): The tunable lighting system uses LED‐based lamps (Glamox, Norway) that contain three independently controllable LEDs (red, green, and blue). A central light controller allows light exposure to be programmed to dim the green and blue LEDs in each lamp to achieve an amber colored light that has negligible blue frequencies (and exposure has been tested using a light spectrometer in different parts of the ward). Individuals are also provided with blue‐blocking screens that can be attached to the front of all electronic devices. At 18:00 a 30‐minute transition period starts where the lights are changed to the blue‐depleted amber color. From 18:30 to 06:50 the light is amber. At 06:50 a new 10‐minute transition changes the light color to ordinary indoor lighting. From 07:00 to CONDITION: Healthy individuals ; Not Applicable PRIMARY OUTCOME: Melatonin levels assessed using saliva samples: Timing of Dim Light Melatonin Onset (DLMO) after 5 days residency in each ward as compared to baseline; melatonin levels on the 5th evening in each condition compared to melatonin levels in dim light on the 6th evening (melatonin suppression) INCLUSION CRITERIA: 1. Age 20‐30 years 2. No evidence of circadian dysrhythmia (defined as a self‐reported bed‐time of about 2300h/2400h and rise‐time of about 0700h/0800h and <2 hours variation in bed‐time and rise‐time between weekdays and weekends 3. Normal color vision 4. No known physical or mental disorder 5. No known family history of severe mental disorder (e.g. unipolar, bipolar, psychotic disorders, etc) 6. Not currently being prescribed any medication SECONDARY OUTCOME: ; 1. Sleep, assessed using: polysomnography on the 4th and 5th evening in each condition; actigraphic recording of sleep‐activity cycles and self‐rated sleep diaries for 1 week prior to residing at the unit and throughout the study period; Xethru radar assessment of movement when participants are in their rooms, including sleep‐activity cycle during residency in each ward; 2. Sleepiness, assessed using: Karolinska Sleepiness Scale scored every second hour from 1800h to bedtime and again at 0700h; EEG drowsiness test at 2100h and 2200h the final two evenings in each condition along with Karolinska Sleepiness Scale at 2100h and 2300h; 3. Neurocognitive function, assessed using Connors Continuous Performance Test 3 on the third evening in each condition; 4. Color discrimination, assessed using the Farnsworth‐Munsell 100 hue test on the first evening in each condition; 5. Acceptability of lighting, assessed using self‐report questionnaires on the first evening in each condition and the final evening in each condition; 6. Perceived side‐effects of residing in each ward assessed using the UKU questionnaire the day after each condition (6th day);