The Hidden Power of Light

By Ingrid Fetell Lee

In the late 1990s, Milan psychiatrist Francesco Benedetti began to notice a curious pattern in the inpatient stays of patients with bipolar disorder at the facility where he worked. The patients with east-facing rooms were discharged more quickly than those in west-facing rooms. There was nothing different about the rooms except for the direction, and patients were randomly assigned. So Benedetti began to wonder: could there be something about the morning light coming in through those eastern windows that was helping patients recover more quickly?

He and his colleagues analyzed the data for 187 bipolar patients who had stayed in the hospital and discovered that a little extra morning light actually had a big effect. Patients with east-facing rooms stayed in the hospital 3.67 days fewer, on average, than those with west-facing rooms.

One of the most surprising areas of my research for Joyful has been discovering just how much research about the influence of light on our wellbeing. Light regulates our Circadian rhythm, the 24-hour sleep-wake cycle that defines the rhythm of our lives. A bewildering array of biological processes are calibrated by the presence of light in our surroundings, from our metabolism to immune function to levels of cortisol in the body. Without sufficient light at the right times, these cyclical processes can fall out of sync, with a host of consequences that researchers are still discovering.

In this post, I’m going to dive into some of the research on the effects of light on your health and happiness to help you harness the power of light to increase your own wellbeing.

This would be a good time to note: In this post I’m going to be talking about some serious mental health conditions, including depression, bipolar disorder, and Alzheimer’s. As always, please remember that this website does not provide medical advice, and that if you or someone you love is suffering from one of these conditions, please consult a trained mental health professional before changing therapies or trying new approaches.

Light may help alleviate depression and bipolar disorder

Light therapy has long been a standard treatment for seasonal depression. (You probably know someone who has one of those light therapy lamps, especially if you live in the northern hemisphere.) But research shows that it might be effective for non-seasonal depression too. A meta-analysis of studies shows that light therapy can be so effective in treating non-seasonal depression that the impact is comparable to that of many anti-depressants. I had to read this finding three times before I processed it. 13 percent of Americans take anti-depressants, which can be costly and come with side effects such as nausea, weight gain, fatigue, and insomnia. Meanwhile, light therapy is inexpensive, accessible, and has very few side effects.

In Japan, the power of light has been applied with remarkable success to address a persistent problem: suicides in train stations. (The country averages one such incident a day.) To combat the problem, Japanese railways have been working to install protective barriers at the platform edges, but these are expensive to construct and structural issues prevent them being installed in every station. So the railway companies began installing LED panels that emit blue-toned light at the ends of the platforms, generally the most isolated spots. Research from the University of Tokyo shows that the “mood lighting” has yielded an 84% reduction in suicides in train stations over a ten-year period. Stations in the UK have begun implementing a similar program, and have also found anecdotal evidence of other benefits, including a reduction in a littering and vandalism.

And of course, there is also the growing body of research on light therapy and bipolar disorder. Research by Benedetti, the psychiatrist who observed the connection between morning light and bipolar disorder, and others suggests that bright light therapy, alone or in combination with other treatments, can have a significant effect on symptoms of this condition. It also seems to present a low risk for the side effect known as hypomania, comparable to placebo treatment and significantly lower than with antidepressants.

Why don’t we hear more about the potential benefits of light? Researchers note that more research is needed on this form of therapy, but because light doesn’t have the same obvious financial upside as pharmaceuticals, studies about light attract less funding.

Light makes us more alert and energetic

As diurnal animals, we are tuned to the rhythms of the sun. For centuries, the mechanism behind this synchronization was a mystery. But in 2002, researchers discovered that our eyes have specialized photoreceptor cells containing a pigment called melanopsin, which senses the quantity of light in our surroundings. This in turn helps to regulate our body temperature, as well as levels of the hormones melatonin (which increases at night to make us sleepy) and cortisol (which rises in the morning, increasing blood sugar and getting us going for the day to come). Melanopsin is most sensitive to light in the bluer part of the spectrum, which is particularly abundant in the morning.

Daylight promotes the optimal balance of hormones for alertness. (This is why travelers are often advised that the best way to beat jet lag is to spend as much time outside as possible during the first few days of a trip.) In dim light conditions, melatonin breaks down more slowly, resulting in a kind of groggy feeling. If you have trouble waking up in the morning, you may want to leave the shades partially open to allow for light to filter in as the sun rises. Or, if you have little natural light in your space, add some bright, broad spectrum lights to your space to compensate. Research shows that bright environments translate pretty directly into increased alertness. And if you find yourself working a night shift, you may want to turn on an extra lamp or two. In a study of sleep-deprived subjects, bright light helped improve mood, motivation, and alertness during the nighttime hours.

Light helps us sleep better

Wait, didn’t I just say that light helps us wake up? And don’t we know that too much light before bed interferes with sleep? True and true, but with light exposure, it’s all in the timing. And it turns out that when we get more light exposure during the day, it not only makes us alert at the time, but it also helps us sleep better at night.

In a study of office workers, those who had significant daylight exposure in their workspace slept an average of 46 minutes longer than those who had no daylight. They also had fewer sleep disturbances in the middle of the night. Other studies have shown that increased daylight or bright light helps to improve sleep for residents of long-term care homes. And light therapy is also being studied as a remedy for sleep disturbances and depression associated with menopause. So if you’re struggling with insomnia, a surprising remedy may be to go for a walk first thing in the morning, increase the light at your desk, or take a lunch break in a sunny spot.

Light improves physical health

In that study of office workers just mentioned, not only did having a sunny desk improve sleep; it also correlated with increased physical activity. Other studies with young people show a similar correlation. It’s not clear whether increased light leads to higher activity levels, or whether being outside leads to greater light exposure and increased activity, but regardless, the two seem to go hand in hand.

Light is also associated more broadly with our physical health and immune responses, both because of its effects on hormone levels and its role in the production of vitamin D. Studies have shown that children in classrooms with full-spectrum and UV-supplemented light miss fewer days of school due to illness, have lower rates of tooth decay, and even grow faster than kids in dimly lit classrooms. (The difference in one study was about .8 inch over two years.) Sunlight also plays a role in warding off osteoporosis in adults, because vitamin D is so critical to bone health. And sunlight may also help to lower blood pressure, by altering levels of a compound called nitric oxide in the bloodstream.

“Put the pale withering plant and human being into the sun, and, if not too far gone, each will recover health and spirit,” Florence Nightingale wrote in her Notes on Nursing, and studies do show a connection between light and healing from more serious illness or injury. In a study conducted on a cardiac ICU, patients with sunnier rooms spent an average of 1 day less in the hospital, and had a lower rate of mortality. Another study of hospital patients recovering from elective surgery found that patients who had more daylight in their rooms took 22% less pain medication, experienced less stress, and resulted in a measurable decrease in costs. Light is now also being investigated as a therapy for a range of conditions, with promising early results for Parkinson’s Disease, cancer-related fatigue in cancer survivors, and chronic back pain, among others.

Light improves memory and concentration

One of the first criteria people mention looking for in a new home is natural light. Yet when we choose a new school for our kids or a workspace for ourselves, we often forget to take this into account. But research suggests we should. In a study of daylight in schools, students in brighter classrooms advanced 20% faster in math and 26% faster in reading than those in the dimmest classrooms. Bright artificial light has also been shown to improve concentration in elementary school students.

Light exposure has also been shown to have an effect on memory in those suffering from Alzheimer’s and dementia. In one study, replacing the bulbs in a nursing home with broad spectrum versions decreased both cognitive decline and depression among residents. Animal research may point to one reason why. Studies of rats housed in low-light and bright-light environments suggest that low light weakens spatial memory performance, as measured by a maze task. Researchers believe that light may have an influence on the hippocampus, a brain region critical to memory.

Light increases our joy

Last but not least, light seems to influence not just mental health conditions like depression, but also brightens mood more generally. In 2014, a group of researchers conducted an experiment with nurses in the acute care ward of a Texas hospital. The working conditions were similar throughout the ward, except for one difference: the nurses’ station in the southern wing had big windows through which daylight streamed into the space, while the northern wing had no windows at all. Among other findings, researchers recorded an higher rate of “spontaneous laughter” on the southern wing. It seems that even amid the stress of their jobs, nurses exposed to more light exhibited more joy.

One potential reason for the connection between light and joy is serotonin, a neurotransmitter involved in the regulation of mood. Sunshine stimulates the production of serotonin, and research shows that most adults exhibit elevated serotonin levels in late summer and fall, after a period of longer days, and reduced levels in early spring when the days are shorter.

Whew! It’s an awful lot of benefits from something that we find just by going outside. But the thing is, though light is freely available, most of us are actually not getting enough of it. Americans spend roughly 87% of our time indoors, and another 6% in cars. That means on average we’re spending less than 2 hours outside per day! Most of us work indoors, in offices and factories housed in big, dense buildings with limited daylight penetration. And while bright, broad-spectrum artificial light can provide many of the benefits of sunlight, lighting standards in offices and public buildings are usually based on cost and energy efficiency, not our health. (And most of these standards pre-date the current wave of research on light and wellness.)

The result is that indoor illumination is typically less than ten percent of the light available outdoors in the shade on a sunny day. To put it in stark terms: the sum total of light exposure you get in sixteen hours spent indoors is likely less than spending even just one hour outside. So I hope this post serves as inspiration to venture out into the sunshine this weekend. Your mind and your body will thank you! And for more practical tips on letting light into your space and daily activities, stay tuned for this month’s Joyletter. Sign up here to make sure you don’t miss it!

February 15th, 2019


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    Discussion (2 Comments)

  1. jorge vede on February 19, 2019


  2. Mervin on January 11, 2020

    Awesome blog! Do you have any suggestions for aspiring writers?
    I’m hoping to start my own website soon but I’m a little lost on everything.
    Would you propose starting with a free platform like WordPress or go for a paid option? There are so many options out there that I’m completely confused ..
    Any tips? Bless you!


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