Out of the blue? How the colour of light could be used to treat mental illness
In Trondheim, a psychiatric unit tested a lighting system that blocks blue wavelengths after 6 pm. Over 400 patients showed quicker clinical improvement and reduced aggression compared with standard lighting. The results suggest that circadian‑aligned lighting could become a simple, drug‑free treat…
In the quiet city of Trondheim, a psychiatric ward has quietly revolutionised patient care by turning the lights on its own side. After sunset, special filters slide over windows and the room dims to a warm amber glow, effectively removing the blue wavelengths that most strongly influence the body’s internal clock. The experiment, carried out by researchers at St Olavs Hospital and the Norwegian University of Science and Technology, aimed to see whether such a change could help patients with acute mental illness feel better and behave more calmly.
How light shapes our mental health
Light is the primary cue that synchronises the circadian rhythm – the roughly 24‑hour biological clock that regulates sleep, hormones, mood and many other bodily functions. When the rhythm is out of sync, a host of problems can arise, from depression and cardiovascular disease to the erratic sleep patterns that often accompany bipolar disorder. In people with severe mental illness, circadian disruption is common, and research suggests that they are especially sensitive to the timing and spectrum of light exposure.
Dr Daniel Smith, a psychiatrist at the University of Edinburgh who leads the UK Circadian Mental Health Network, notes that evening light can delay the circadian phase, suppress melatonin and push people to stay up later. Poor sleep, in turn, can destabilise daily routines and trigger mood episodes. Although the idea of using light to stabilise rhythms has long been discussed, large clinical trials have been scarce.
The Trondheim experiment
When the new psychiatric unit was being designed, the team seized the opportunity to test a blue‑depleted lighting system in a real‑world setting. The ward was split into two identical halves, each with the same layout, staffing and facilities. The only difference was the lighting in the evening: one side switched to amber light at 6 pm and used blinds and filters to block blue light from windows and screens; the other side retained standard hospital lighting.
In a pilot study with healthy volunteers, the researchers observed changes in melatonin levels, sleep timing and alertness that confirmed the expected physiological effects of the lighting change. Building on that, they enrolled 476 patients admitted for short‑term psychiatric intensive care. These patients had conditions ranging from psychosis and mania to severe depression and suicidal thoughts.
Half of the patients were assigned to the blue‑depleted ward and the other half to the control ward. The average length of stay was similar – three to four days – but the outcomes were strikingly different. Those in the amber‑light environment showed greater clinical improvement, were more likely to be in a mild disease state at discharge, and exhibited noticeably less aggressive behaviour.
Why aggression matters
In acute psychiatric settings, aggression and agitation pose serious risks to both patients and staff. Studies estimate that aggressive incidents occur in anywhere from 8 % to 76 % of cases. Reducing such incidents can improve safety, reduce staff stress and lower the likelihood of medication escalation.
Dr Håvard Kallestad, who led the research, emphasized that the lighting intervention was “zero burden” for patients – they did not have to wear glasses or sit in front of a light box. Instead, the environment itself was engineered to align with human biology. This makes the approach scalable and easily integrated into existing hospital designs.
Beyond the ward: wider implications
The findings have sparked interest in applying circadian lighting to other settings. The UK’s National Institute for Health and Care Research has called for trials to test whether similar lighting could help residents in care homes, potentially reducing behavioural disturbances in dementia. Meanwhile, neuroscientist Prof Colleen McClung suggests that personalised light therapy – morning exposure for those with delayed rhythms, evening exposure for those with advanced rhythms – could be guided by wearable sleep trackers.
Such strategies could offer a cost‑effective, drug‑free complement to traditional treatments, improving sleep, mood and overall quality of life for people with mental illness.
What’s next?
While the Trondheim study provides compelling evidence, larger, multi‑centre trials are needed to confirm the benefits across diverse populations and settings. If replicated, the blue‑depleted lighting model could become a standard feature of psychiatric wards worldwide, offering a simple yet powerful tool to support mental health recovery.
Why it matters
By harnessing the natural influence of light on circadian rhythms, hospitals can enhance treatment outcomes and reduce aggression without additional medication, improving safety and patient well‑being.
Key points
- Blue‑depleted lighting reduces aggressive behaviour in psychiatric wards
- Patients in amber light show faster clinical improvement
- The intervention is low‑cost and patient‑friendly
- Circadian lighting could be applied in care homes and other settings
- Personalised light therapy may tailor treatment to individual rhythms
Frequently asked questions
What is blue‑depleted lighting?
It is a lighting system that blocks blue wavelengths after a certain time, usually in the evening, to reduce the impact on the body’s circadian rhythm.
How does it help patients?
By aligning light exposure with the body’s natural clock, it can improve sleep quality, mood, and reduce aggressive behaviour.
Is it safe?
Yes, the study found no adverse effects; patients did not need to wear special glasses or use light boxes.
Can it be used outside hospitals?
Researchers are exploring its use in care homes and other settings to manage behavioural disturbances and improve sleep.
