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Being in the Pacific Northwest, most people are aware that sun exposure in this region is not optimal, and as such, Vitamin D levels trend on the lower side. It has been established that Vitamin D has links to mood (1,2), but recent studies have found that it’s more than just vitamin D that we get from the sun. It’s actually being found that direct light exposure into the eyes (specifically the retina) is also positively linked to mood (3,4,5,6).

Phototherapy is defined as using light to treat mental or physical illness. A specific form of this, called Bright Light Therapy (BLT), is being studied to treat an array of mood disorders including Seasonal Affective Disorder (SAD), Major Depressive Disorder (MDD), Bipolar Disorder (BD), Postpartum Depression, and Premenstrual Dysphoric Disorder (PMDD) (3,4).  The American Psychiatric Association practice guidelines actually list BLT as an alternative to or in addition to pharmacologic and psychological treatment in some of these conditions (3).

When you think about it, light therapy seems rather straightforward and simple. We usually think “just get out in the sun”. However, studies are showing that timing, quantity, and position are all very important when it comes to efficacy (4,5). This is one of the many reasons why it is important to talk to your physician about this before starting treatment on your own, as the timing and duration of these are different dependent on your specific symptoms.

BLT is showing to have many benefits, but I’d like to specifically focus on light therapy as a treatment for depressive episodes of Bipolar Disorder. One of the hardest things about BD is that there are a limited range of first-line medications available for treatment and it often takes a long time of trial and error before finding the right combination and dosage for each individual. This leaves a lot of frustrating months suffering from medications either being ineffective or having intense side effects, or both. There are also limited studies available for nutritional or supplemental treatments and advice is often theoretical. Even though these treatments, when adhered to, are clinically found to be effective, this is also a process of trial and error that can take months — and cost a pretty penny along the way.

One of the great things about light therapy is that many people will notice within 2-4 weeks whether or not it is going to be effective for them. It can also help to maintain a stable state, so those months of hard work finding the right combination of nutrition, lifestyle, medications, and/or supplements are supported for long term health and stability.  Another reason it’s important to discuss this option with your provider is that this therapy, like many antidepressants, has the potential to trigger a manic or hypomanic episode (3,4,5). Fortunately, unlike some medications, it’s very easy to stop or adjust your dose.

So, how does it work? Well, the typical answer to this question still applies here: the mechanism isn’t fully understood. But we do know that light activates part of the retina which sends a signal to the hypothalamus – an area in the brain that helps to regulate mood. This is thought to be involved in how it works as a therapy.

The treatment typically consists of a light box positioned at, or above eye level, with light pointing downward into the eye. The reason it needs to shine down into your eye is that the receptors that “see” light as a signal that it’s daytime are located on the bottom of your retina (makes sense when you think about how sunlight shines down at us) (5). The dose you get depends on what kind of light box you’re using (size and light strength), how close it is to your face, and if it’s positioned above or below your eyes. The larger the box the better it is, due to more coverage and exposure regardless of head movement. Full spectrum light at the strength of 10,000 lux is what is commonly used in studies.

The safest way of introducing any new modality in your life is to start low and go slow. An approach that one psychiatrist suggests, specifically for Bipolar Disorder, is starting at 15 minutes midday. If after 4 days there is no noticeable effect, increase to 30 minutes at midday. If after 4 days absolutely nothing has changed, move the timing back by one hour earlier in the day. Then you can continue moving it back by 1 hour every 4 days until it is aligned with the time you wake up. If it works well at midday, keep it there. Midday exposure can help with a higher melatonin surge at night which helps support better sleep onset and maintenance – another cycle closely related to BD (3).

Options to purchase include light boxes of various sizes and strengths, or a light visor – although it’s good to keep in mind that none of the studies were done using vizors (but the same principle applies).

There are a few side effects to be cautious of, and these include (4):

  • Eye strain
  • Headaches
  • Induction of manic or mixed-state in BD. Symptoms can include:
    • Agitation
    • Irritability
    • Insomnia (typically occurs if light exposure is in the latter half of the day)
    • Increased and rapid thinking
    • Difficulty concentrating

It is important to watch for these symptoms when undergoing this treatment. If they show up, you should stop the treatment and discuss further steps with your provider.

People who should be cautioned against this treatment, or be closely monitored by their healthcare professional, include those (5):

  • with macular degeneration or family history of macular degeneration
  • with porphyria, lupus, actinic dermatitis, or solar urticaria
  • who take medication that sensitizes them to light, phenothiazines, some antiarrhythmic medications, some psoriasis treatments, antimalarials, St. John’s Wort, or medications for rheumatoid disease

Want an easier way to try this without having to commit any time to your day? Try a dawn simulator first. This has not yet been associated with causing mania or hypomania, does not have any associated risks, and takes no extra time out of your day since treatment is over as soon as you wake up (5).

It involves a lamp that gradually brightens over a set period of time in the morning to help you transition from sleep into wakefulness. The great thing is that the light is still getting to your retinas, even while you are sleeping (5). Other possible benefits of this method include improved morning cognitive function and helping to regulate the sleep-wake cycle.

If you’d like to read more information about dawn simulators, here’s a great resource:

~Dr. Jordan McLendon


  1. Penckofer S, Kouba J, Byrn M, Estwing Ferrans C. Vitamin D and Depression: Where is all the Sunshine? Issues in Mental Health Nursing. 2010;31(6):385-393. doi:10.3109/01612840903437657
  2. Spedding S. Vitamin D and Depression: A Systematic Review and Meta-Analysis Comparing Studies with and without Biological Flaws. Nutrients. 2014;6(4):1501-1518. doi:10.3390/nu6041501
  3. Nasr SJ, Elmaadawi AZ, Patel R. Bright light therapy for bipolar depression.
  4. Purse M, Gans, S. Light Therapy for Bipolar Disorder. Verywell Mind. Published 2020. Accessed July 23, 2020.
  1. Phelps J. Light therapy for bipolar depression. Published 2019. Accessed July 22, 2020.
  2. Sit DK, McGowan J, Wiltrout C, et al. Adjunctive Bright Light Therapy for Bipolar Depression: A Randomized Double-Blind Placebo-Controlled Trial. AJP. 2018;175(2):131-139. doi:10.1176/appi.ajp.2017.16101200
  3. Liebson E. Can light therapies help with bipolar disorder? – Harvard Health Blog. Harvard Health Blog. Published 2020. Accessed July 22, 2020.

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