Ever thought that the colour of the lights around you could influence your mental health? A psychiatric unit in Trondheim, Norway, is currently testing whether changing the lighting environment in hospital wards can help people recovering from severe mental health conditions such as psychosis and depression.
The approach is based on a simple but intriguing idea: light strongly influences the body’s internal biological clock. In this experimental ward, the lighting environment is designed to mimic more natural patterns of light and darkness. As evening approaches, filters are lowered over windows and the indoor lights gradually shift to a soft amber tone that removes most blue wavelengths.
Blue light, which is commonly emitted by LED lights and digital screens, is known to interfere with the body’s circadian rhythm - the roughly 24-hour internal clock that regulates sleep, hormones, and many biological functions. By reducing blue light exposure in the evening, researchers hope to stabilise patients’ biological rhythms and improve psychiatric symptoms.
The findings from this experiment, published in the journal PLOS Medicine, suggest that while changing evening lighting may not shorten hospital stays, it could modestly improve clinical outcomes for people admitted to psychiatric wards.
How was the study conducted?
The research was designed as a large randomised controlled trial to test whether modifying evening light exposure could influence outcomes in people admitted to acute psychiatric care.
As the researchers noted, “The impact of light exposure on mental health is increasingly recognised. Modifying inpatient evening light exposure may be a low-intensity intervention for mental disorders, but few randomised controlled trials exist.”
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To examine this possibility, scientists conducted the study at a psychiatric hospital in Trondheim, Norway. Between October 2018 and March 2019, and again between October and November 2019, adults admitted to the hospital’s acute psychiatric ward were randomly assigned to one of two environments.
One ward was equipped with a blue-depleted evening light environment, where lighting was specifically designed to minimise blue wavelengths in the evening hours. The other ward maintained a standard lighting environment, similar to conventional hospital lighting.
The blue-depleted environment was implemented using several adjustments. Lights were designed to emit minimal blue light in the evening, filters were placed over windows to block blue wavelengths, and additional filters were installed on televisions and digital devices. These measures aimed to reduce the type of light known to interfere with the body’s circadian rhythm.
In total, the study included 476 patients, with an average age of 37 years. Among them, 41 per cent were male and 59 per cent were female. Researchers analysed several outcomes, including the length of hospital admission, improvement in symptoms, illness severity at discharge, aggressive behaviour during hospitalisation, and patient satisfaction.
What the study found
The primary outcome of the trial was the duration of hospital admission. However, the results showed no meaningful difference between the two groups. Patients exposed to blue-depleted lighting stayed in hospital for an average of 7.1 days, compared with 6.7 days for those in the standard lighting environment. The estimated difference of 0.4 days was not statistically significant.
Despite this, the researchers observed improvements in several secondary outcomes. Patients in the blue-depleted light environment showed greater clinical improvement during admission, as measured by the Clinical Global Impressions Scale. They also had lower illness severity at discharge compared with patients exposed to standard lighting.
In addition, the study found lower levels of aggressive behaviour among patients exposed to the modified lighting. The researchers reported that predicted serious aggressive events were nearly three fewer per 100 days of hospitalisation in the blue-depleted lighting ward.
The clinical significance of these findings was evaluated using a metric known as the Number Needed to Treat (NNT), which estimates how many patients must receive a treatment for one person to benefit. For improvements in symptoms, the NNT was 12, while the NNT for reduced illness severity at discharge was 7.
“These clinical benefits were achieved without any discernible differences in patient-rated side effects or treatment satisfaction levels,” the researchers noted.
Importantly, the study did not find differences in other outcomes, including suicidality, violent incidents, or the likelihood of patients shifting from involuntary to voluntary admission status. However, the authors noted that such events occurred relatively rarely in the study population, meaning the trial may not have been large enough to detect small differences.
Researchers also emphasised that the trial was designed to reflect real-world clinical conditions rather than a highly controlled laboratory environment. The hospital serves a population of around 300,000 people, and the patient group was diverse, including individuals with a wide range of psychiatric diagnoses and complex health needs.
Over the eight-month recruitment period, the ward recorded 1,118 admissions, with a median hospital stay of about four days. Nearly half of these patients were recruited into the study, including individuals admitted involuntarily or with severe psychiatric conditions who are often excluded from research trials.
Because of this design, the researchers believe the findings may be more generalisable to real clinical settings than many smaller studies conducted in specialised clinics.
Although the intervention did not shorten hospital stays, the results suggest that altering lighting conditions could provide modest therapeutic benefits.
The researchers added that “the NNTs for greater clinical improvements and lower levels of aggressive behaviour are similar to other low intensity interventions employed in psychiatry and in general medicine.”
The authors believe these findings provide “some cause for optimism” that modifying hospital lighting could benefit patients in psychiatric wards.
Limitations of the study
Despite the encouraging findings, the researchers acknowledged several limitations. One major issue was that the design of the study made it impossible to blind patients or clinical staff to the lighting conditions. As the authors noted, “the nature of this study meant it was impossible to blind patients or clinical staff to the lighting condition,” although they found no evidence that bias influenced discharge decisions or clinical evaluations. The study also observed differences in staff assessments of behaviour but not in objective outcomes such as recorded violent incidents, partly because such events were rare.
The trial also faced participation and data challenges. Due to the use of deferred consent, some patients left before they could be approached for participation, while others did not sign consent forms. As a result, “about 50% of all admitted patients were included in the ITT population.” In addition, some baseline data were incomplete, likely because patients’ mental health conditions affected their ability to provide information.
Despite these limitations, the researchers said the results suggest potential benefits of modifying hospital lighting. They concluded that “changing the evening light environment moderately enhances the clinical outcomes of standard acute psychiatric hospital inpatient care,” but emphasised that further research is needed to determine the optimal exposure and which patients may benefit the most.
What experts say
Explaining the science behind the findings, Dr Vivian Kapil, Consultant Psychiatrist at SRM Prime Hospital, said that what researchers describe as blue-light exposure is commonly linked to prolonged screen use from devices such as mobile phones, laptops and tablets.
According to Dr Kapil, such exposure can disrupt the body’s natural biological clock. He explained that the human body follows a roughly 24-hour cycle known as the circadian rhythm, which regulates sleep and several other physiological processes. “Our body has its own biological clock, which we call the circadian rhythm. When people are exposed to blue light from screens at night, it can reset this biological clock,” he said.
Reducing exposure to blue light in the evening can help the body recognise when it is time to wind down. “When blue light exposure is reduced, the body realises that it is night-time. This helps improve sleep and also supports better regulation of mood,” Dr Kapil said. In contrast, excessive screen exposure late at night can confuse the body’s internal clock. “When we continue to look at screens at night, the body does not clearly recognise whether it is day or night, and that is why we advise limiting screen exposure before sleep.”
Dr Kapil added that environmental changes such as adjusting lighting conditions could support psychiatric care, but they should be viewed as complementary rather than primary treatments. “The mainstay of treatment for mental health conditions remains psychotherapy and medications,” he said. “Environmental modifications, such as limiting blue-light exposure or changing lighting environments, can act as supportive interventions alongside these treatments.”
He also pointed out that the study was conducted in acute inpatient psychiatric settings, where patients are often severely unwell and receiving intensive medical care. Because of this, the results should be interpreted with some caution. “In acute wards, patients are usually very unwell and receiving intensive treatment. So lighting changes would be one of several supportive interventions rather than a standalone therapy,” he noted.
Beyond hospital settings, however, Dr Kapil believes that reducing blue-light exposure could benefit the general population as well. “Sleep is one of the best and most accessible forms of therapy,” he said. Poor sleep caused by excessive screen exposure can contribute to several mental health problems, including depression, anxiety and mood disorders.
“For mental well-being, limiting blue-light exposure, especially from screens, is very important,” he added. “This should not only be practised in hospitals but also at home to support better sleep and overall mental health.”
This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS