Humans (and other creatures) instinctively gravitate towards sunlight – for warmth, illumination, energy, and a sense of well-being. But there’s also a strong scientific reason that we crave natural daylight: the outdoor day-night cycle is essential to maintaining normal, healthy physiology.

The importance of light – beyond vision – has been known in all cultures for a very long time. The scientific research effort however, is recent. It was inspired by findings that light exposure directly affects levels of melatonin and serotonin and can reset the body's clock either forward or backward.

Bright light therapy – which involves daily, scheduled exposure to intense levels of natural or artificial light – is the first-line treatment for seasonal affective disorder and is also effective for non-seasonal depression and bipolar depression.^1-8 Even in the absence of a mood disorder, light therapy may be beneficial for maintaining a healthy mood state for anyone who experiences sadness, fatigue, or disrupted sleep patterns during the winter months.

Related: 6 ways to boost your mood this winter

Related: Natural remedies for anxiety and depression

Sources:
The efficacy of light therapy in the treatment of mood disorders: a review and meta-analysis of the evidence
Adjunctive bright light therapy for treating bipolar depression: A systematic review and meta-analysis of randomized controlled trials
Light therapy for non-seasonal depression: systematic review and meta-analysis
The Efficacy of Light Therapy in the Treatment of Seasonal Affective Disorder: A Meta-Analysis of Randomized Controlled Trials

How bright light therapy works

Scientists think that light therapy works at several different levels, producing a combined beneficial effect. First, light exposure is directly energizing for most people, thus combating mood-associated fatigue. Sunlight also increases the production of beta-endorphin, a mood-enhancing substance, in the skin.⁹

In a natural environment, upon waking you would be exposed to the brightness of natural sunshine. The blue wavelengths from sunlight enter the retina where they act as a circadian signal, telling the body to reduce synthesis of melatonin (sleep neurotransmitter) and stimulate the production of serotonin, the alert and feel-good neurotransmitter.³ When you are not exposed to light early in the day, the continuation of melatonin secretion could upset your body's natural rhythm and sleep pattern.

Sources:
Beneficial effects of UV radiation other than via vitamin D production
Bright Light as a Personalized Precision Treatment of Mood Disorders

The connection between depression and circadian rhythms

Depression – whether seasonal or not – has a circadian component. People with depression often suffer from insomnia, wake excessively early, have diminished sleep quality, or have delays in melatonin onset. There is also evidence that the circadian rhythm of the autonomic nervous system, as well as the balance between sympathetic and parasympathetic activity is disrupted in depression.¹⁰

Get sunlight on your face

Sunlight exposure first thing in the morning is the most effective form of light therapy. Sit with the sun shining on your face or take a walk toward the sun. The sun will indirectly penetrate the iris and affect the brain. You should not look into the sun, but the sun has to hit your face without sunglasses.

In the early hours, you also get more exposure to infrared wavelengths compared to later in the day. There is evidence infrared exposure has beneficial effects on skin health and mood, and facilitates wound healing.^11,12

After about 9:00 am when the sun gets stronger, protect your skin appropriately from ultraviolet light-related sun damage with clothing or mineral sunscreen.

Related: Podcast: Are you getting enough sunshine, vitamin D, and calcium?

Related: Chemical sunscreens are even worse than we thought

Sources:
Bright light therapy for depression: a review of its effects on chronobiology and the autonomic nervous system
Infrared and skin: Friend or foe
Transcranial and systemic photobiomodulation for major depressive disorder: A systematic review of efficacy, tolerability and biological mechanisms

Cold weather alternative: therapeutic light

During fall and winter, when it is not bright outside or too cold to be outside in comfort, a therapeutic light that mimics full-spectrum sunlight can be an effective substitute. If you are using a therapeutic light, sit 12-18 inches away for about 30 minutes, early each morning.¹

When used at an appropriate morning hour (or in rare cases, evening hour), therapeutic lights:

Correct the misalignment of the internal body clock with external night and day
Improve sleep patterns
Stimulate the brain's production of neurochemicals that elevate mood and well-being
Work like a natural antidepressant, without side effects or interactions with medications, and starts working quickly.¹⁰

Light therapy and nutrition

I recommend combining light therapy with a high-nutrient diet and omega-3 fatty acids (DHA and EPA) supplementation. Learn more here: Natural remedies for anxiety and depression

Related: Short-term dietary intervention improves depression symptoms

I have researched the therapeutic lights on the market, and I recommend this Carex Therapeutic Light which contains the features that medical literature reveals are critical to the effectiveness of light therapy.

Sources:
Seasonal affective disorder
Bright light therapy for depression: a review of its effects on chronobiology and the autonomic nervous system