Nighttime light exposure may increase your risk of developing psychiatric disorders, a new study shows.

Maintaining a healthy circadian rhythm can play an important role in mental health, and when that rhythm becomes unbalanced the body can respond in negative ways.

New research published this month in the journal Nature Mental Health found that individuals who consumed more light at night had an elevated risk of anxiety, bipolar disorder, and PTSD severity as well as self-harm risks.

The study also found that increasing exposure to daytime light can reduce psychosis risk by working as a non-pharmacological means of improving mental health.

“Our findings confirm that the most healthy light patterns are the more natural patterns of bright days and dark nights,” Sean Cain, PhD, one of the authors of the study and an associate professor at the Monash School of Psychological Sciences and the Turner Institute for Brain and Mental Health, told Health.

“This is the type of light we evolved under and what our bodies expect,” he said.

Here’s how the time of day you’re exposed to light impacts mental wellbeing, and how to optimize light for the good of your circadian rhythm.

To better understand the role of light and how it affects the body’s natural rhythm and mental health, the research team conducted an 87,000-person, cross-sectional analysis of light, sleep, physical activity, and mental health.

Participants were recorded for one week while undergoing light monitoring and rest cycles to understand how light exposure during the day and night was associated with various psychiatric disorders that could be linked to disrupted circadian rhythms.

Following light exposure, participants were given a mental health questionnaire to acquire more information on potential psychiatric outcomes.

What they found was that those exposed to high amounts of light at night had an increased risk of depression by 30%, while those who were exposed to high amounts of light during the day reduced their risk of depression by 20%.

Results were similar for PTSD, generalized anxiety disorder, self-harm behaviors, bipolar disorder, and psychosis.

“Mental illness is often worse at night,” said Cain. “As light makes us feel better, it likely draws us to use more light. In the short term, we may feel better, but in the long term, it’ll disrupt our rhythms and likely lead to poorer mental health.”

Exposure to light during the day can strengthen the body’s internal clock—the circadian rhythm. This exposure can help organize the body’s physiology, while light at night has the opposite effect—it weakens your body’s clock.

Virtually all the tissues of your body have daily rhythms that are controlled by a 24-hour clock at the base of your brain. This clock expects light in the day and darkness at night. Contrary signals (dim days and bright nights) can disrupt this cycle and hinder your brain’s ability to properly follow a natural rhythm.

When these signals get crossed, the body’s natural rhythm and sleep-wake routine can be thrown off track and create severe sleep problems like insomnia, issues with hypertension, obesity, stroke, heart disease, gastrointestinal issues, and more.

But not all light is the same.

“Natural light is generally much brighter,” said Cain. “It’s difficult for us to tell visually just how much different the brightness is because our visual system adjusts our perception of brightness.”

Artificial light, on the other hand, can be made to better mimic the effect of outdoor light on our clocks by having more blue wavelengths. Cain explained that for those who might have to spend time indoors, this would be a good option.

“There is a misconception that blue light is bad,” he said. “Blue light is good in the day, just bad at night.”

While getting as much bright daylight as possible is a good start to maintaining your body’s natural rhythm, getting light at any time throughout the day can have a boosting effect on your body and your mood.

Avoiding all types of light at night is important, but it might not be feasible.

Cain recommends using smart lights that can be set automatically to become very dim and warm, giving a candle-like light.

“This type of light impacts our clocks less,” he said. “If they are set to go dim and warm a few hours before you want to go to bed, you’ll likely find your rhythms naturally locking into that time with little effort.”

Red light therapy has also been shown to be an effective method for supporting your body’s natural clock.

Research from 2019 found that using a combination of red and ambient white light in the afternoon improved circadian rhythm and increased alertness in the study’s 19 participants.

For individuals who might suffer from seasonal affective disorder (SAD), light can also have a major effect on the body’s natural wake cycle and mental health disorders.

Typically, SAD begins during the beginning of winter because days shorten and less daylight causes changes in serotonin and melatonin levels that disrupt the body’s circadian rhythm.

Tatiana Rivera Cruz, LICSW, ADHD advisor and therapist, said in addition to lifestyle habits like exercising, good sleep hygiene, and consuming a healthy diet, red light therapy or SAD lamps can be very beneficial. 

For the most effective results, use lights or lamps that are designed for SAD within the first hour of waking up in the morning, for about 20 to 30 minutes, Cruz explained.

The light can be used throughout the day in short time increments, with more light therapy in the evening, once the sun has set, as another optimal time. People with SAD should stop using light therapy at least one hour before bed. 

“This option is good to use in the winter and you can find better benefits using it before and after daylight exposure,” Cruz told Health. “Light therapy and red light therapy help improve mental health, wound healing, and pain management.”