How Long Does It Take For Light Therapy To Work For SAD?



by Lydia


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To understand how long light therapy will take to work, you need to understand a few concepts around it first, which include:

1. What is Seasonal Affective Disorder (SAD)?

Seasonal Affective Disorder (SAD) is a type of depression that recurs at specific times each year. It is known as a type of Major Depressive Disorder with a seasonal pattern. Patients with SAD will typically experience it during fall and winter when there's little sunlight.

However, some may experience summer SAD, which begins at the onset of spring/summer. Sunlight is the key trigger to Seasonal Affective Disorder, so in the darker months, a lack of sunlight may cause SAD symptoms, while during the brighter seasons, excessive sun exposure may trigger summer SAD.

Generally, Seasonal Affective Disorder is characterized by:

  • Depression
  • Feelings of hopelessness
  • Mood changes
  • Change in the sleep schedule
  • Constant fatigue
  • Lethargy
  • Social withdrawal
  • Cravings for sugary foods and carbohydrates
  • Excessive weight gain/weight loss

Symptoms specific to winter SAD may include:

  • Excessive sleeping
  • Cravings for foods high in sugar or carbohydrates
  • Excessive weight gain
  • Fatigue or low energy

Whereas, the symptoms specific to summer Seasonal Affective disorder may include:

  • Insomnia
  • Poor appetite
  • Excessive weight loss
  • Anxiety or agitation

It's essential that you talk to your doctor if you're experiencing any of these symptoms. Your doctor can also provide recommendations on how to manage stress levels.

2. What is Light Therapy?

Light therapy is one way to treat Seasonal Affective Disorder by exposing the patient to artificial light. Treatment for the SAD condition may include bright light therapy (phototherapy), psychotherapy, and medications.

Your brain uses daylight to set the body's natural clock, which dictates important functions, such as waking up and sleeping. If your body clock, also known as the circadian rhythm, is disrupted, it could trigger Seasonal Affective Disorder symptoms.

3. How Does Bright Light Therapy Work?

Light therapy works by helping balance your circadian rhythm and your body's production levels of melatonin and serotonin.

Melatonin is a neurotransmitter hormone made by the brain when it's dark. This hormone helps you fall asleep at night. During periods of low sun exposure, people with this syndrome may have high melatonin levels, because their brain doesn't receive the proper environmental signals to stop producing the chemical, which causes excessive feelings of sleepiness or sluggishness.

Serotonin is the hormone that influences your appetite and mood. Production of this hormone can also be affected by lack of sunlight. Low production of serotonin could result in feelings of depression.

Light therapy systems can treat SAD and alleviate symptoms of other conditions, such as circadian rhythm sleep disorders, jet lag, and even dementia. During these sessions, you sit near a light device called a light therapy box. The light box contains fluorescent bulbs that give off a bright white light of 10,000 LUX, mimicking natural sunlight. This light is approximately 5 to 20 times the intensity of light levels found in indoor lighting.

4. Does Bright Light Therapy Work?

Clinical research shows that light therapy has helped treat 50-80% of people with SAD. From the first controlled light therapy research study in 1984, more than 60 controlled research studies have been published worldwide. Experts are confident that bright lights work for the majority of people with SAD.

Studies also show that many people positively respond to light box therapy within the first week or 3-5 days. If you don't respond to treatment within that time frame, you may notice an improvement in the second week. Long trials have also shown an increase in positive response rate to the bright light therapy after two weeks, with incremental improvements in the third and fourth week. Therefore, it's recommended the patient diligently continue using the bright light therapy system for at least one month to conclude whether it's helpful or not.

Similarly, patients may experience a recurrence of SAD symptoms, such as depression, if they stop using the bright light therapy system. For the light therapy treatment sessions to work, a health professional may advise using light therapy for at least 30 minutes every day.

Although light boxes are effective and safe for SAD treatment, they are not approved or regulated by the Food and Drug Administration. However, the Center for Environmental Therapeutics has issued requirements that your light box should meet to offer effective light box therapy.

Make sure your light therapy box meets these specifications:

  • Clinically tested to treat SAD, since other light boxes are designed to treat skin disorders
  • A full-spectrum 10,000 LUX light box
  • Comes with UV screen filters
  • Can be set at an angle for minimal glare
  • Is the correct size for your needs — a larger surface area will mean you don't have to sit so close to your bright light therapy box

Common temporary side effects of using light therapy include headaches, nausea, and eyestrain. You may also experience fatigue due to changes in your sleep-wake cycle, but this will go away after a week. Overuse of the light therapy system could also cause headaches and eye problems.

5. Can I Use Light Therapy for SAD If I Suffer from Macular Degeneration?

This is an eye disorder that occurs when a small portion of your retina, called the macula, thins out. It happens when you get older and is therefore commonly referred to as Age-Related Macular Degeneration. With this condition, you are advised to stay away from UV light.

In this case, you must ensure your light therapy system filters out ultraviolet light and doesn't emit blue light. You should never start this treatment without consulting your doctor. It's necessary to talk to your doctor and eye specialist, as some medicines cannot work with this type of light exposure.

You should also consult your doctor if you have pre-existing conditions, such as:

  • Bipolar disorder — this treatment could bring about adverse effects, such as agitation or hyperactivity
  • Glaucoma
  • Or you've had cataract surgery in the past

6. Does the Therapy Lamp cause Tanning

Therapy lamps designed to treat SAD don't cause tanning since the therapy lamps filter out at least 99.3% of UV light, whereas tanning lights do not. Additionally, the UVA/UVB light rays of tanning lamps can increase your chances of getting skin cancer. For this reason, the use of tanning beds and tanning lamps is not recommended.

With these tips, you should now understand how long it takes for light therapy to alleviate SAD symptoms.


A. Seasonal Affective Disorder: Using Light Therapy:,%2C%20eye%20strain%2C%20and%20nausea

B. Light therapy:

C. Light Therapy FAQs:

D. The Dos and Don’ts of Light Therapy for SAD with Macular Degeneration:

E. 5 Triggers for Seasonal Affective Disorder in the Summer:

F. Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial:

G. Seasonal Affective Disorder:

H. Seasonal Affective Disorder:

I. Physical Exercise in Major Depression: Reducing the Mortality Gap While Improving Clinical Outcomes:

J. How to Select a Light Box:


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