Everything You Need to Know About Light Therapy for Seasonal Affective Disorder (SAD)


The value of light therapy for treatment of Seasonal Affective Disorder (SAD) is well established1, 2, 3, but for those interested in  pursuing this approach, the obstacles are the time to determine which product will be potentially most effective, and how to implement use  to achieve a therapeutic effect.

The purpose of this post is not to contain “everything”, just everything you need to know to how to find a product that works for you, and how to use it effectively (that’s a disclaimer).

My interest in this topic is somewhat personal: as I age, I am becoming aware that during the winter, my mood changes. To describe my mood as “depressed” is a disservice to people experiencing depression. It’s more of a “joylessness” or “flatness” that I begin to notice after a few weeks of dark days (this post is prompted by the consistently gloomy autumn we’ve had this year).

On one hand, this is a part of life (my grandmother had the same experience – she simply accepted it and carried on).

On the other, as someone (Peter Beard, I think) remarked: “I wake up every morning because this is my one and only life” (or words to that effect, I’m paraphrasing from memory). Life is too short to let half the year(/your life) pass feeling flat.

What is the Relationship Between Light and Seasonal Affective Disorder (SAD)?

In a nutshell, the relationship between mood and light is thought to be rooted in our circadian rhythm (although the scientific support for this is at this time not robust2). Certainly, there does exist evidence that secretion of melatonin (a hormone secreted by our pineal gland) and  is disrupted in persons experiencing Seasonal Affective Disorder (SAD).3

The main roles of melatonin in our body are to regulate our sleepiness and wakefulness, and in sexual development.

Melatonin levels respond to the level of light in the environment: it is “turned off” by bright light.5 Melatonin levels are nearly undetectable during the day.5

How Does Light Therapy for Seasonal Affective Disorder (SAD) Work?

If the thought is that low levels of light during the winter, affect melatonin levels, affecting wakefulness and mood, the obvious course is to use a Light Therapy products during the day to replicate exposure to daytime light.


The guideline is 30 to 60 minutes daily of “white light” exposure, between September and April.1

If using a “blue light” product (which is required if melatonin suppression is the goal of Light Therapy use) 45  minutes of morning exposure is the prescription.1

You will notice that most products (at the time of this writing) deliver “white light”, and even the manufacturers customer service professionals appear not to know why a blue light mode is offered on certain devices (“Some people prefer the ‘softer’, blue light”) . Blue light (specifically light in the 446-477 nm wavelength) is required to suppress/regulate melatonin.6

Further, “full spectrum” light, although most closely mimicking natural light, does not offer any benefit with regard to mood, over white light.7

Importantly, although it is blue light specifically that supresses melatonin secretion, white light (full spectrum or otherwise) has proved to benefit mood for those experiencing Seasonal Affective Disorder (SAD).1

What Type of Light Therapy Product to Purchase

Light therapy products have become much more accessible over the years. Early in my practice I recall recommending these products, but the options were very limited, and the cost was in the 300 CAD range (and that’s in early-aughts dollars). Today, many products are available in the 50 to 100 CAD range (a dilemma of a different sort).

Based on the the research to date, important considerations when purchasing a Light Therapy product include:

  1. A blue light option (446-477 nm is the most potent wavelength region providing circadian input for regulating melatonin secretion–  I haven’t seen a product offering this level of detail in their listing; this is more of a “FYI” for if you do). Many products deliver only white light.
  2. 10’000 lux of brightness. Some products deliver less (e.g., 7500 lux).
  3. Ultraviolet (UV)-free light (all the products I have seen are UV light-free).

Other, more personal considerations may include:

  1. Ability to adjust light intensity. I have read reviews that describe certain products as delivering an uncomfortably bright light.
  2. Low glare. Most products I’ve seen appear to be “low glare”, but not all advertise this feature.
  3. Full spectrum light. Although full spectrum light confers no special benefit with regard to affecting mood when compared to white light, it offers what many consider a more pleasant  (natural light-mimicking) light.
  4. Some products may emit a “hum” which may be annoying to some.
  5. Use of LEDs as a light source to minimize maintenance.
  6. Portability. Most of these units are quite small, but some have more a “notebook” design that lends itself to transport for use at home and at work.

This is the product I’ve found that checks the important boxes (PureGuardian SPA50CA Light Therapy Lamp for those reading this after this link has expired).

Apparently it does emit a hum at higher intensity settings, and uses a timer that must be reset after 30 minutes maximum (i.e., you are not able to simply set it beside you and work for an entire afternoon), but those are shortcomings I can live with.

How to Implement a Light Therapy Strategy for Reducing Seasonal Affective Disorder (SAD) Symptoms

As written above, it is blue light specifically that suppresses melatonin. To reduce melatonin levels at waking, to increase alertness and “set” your circadian rhythm for the day, expose yourself to blue light, for 45 minutes at waking.

These devices suggest use at a distance of 6 to 24 inches (ideally seven inches), so depending on your morning routine, you will have to either wake earlier (and retire earlier the night before) to rest, read, meditate, etc. in bed for 45 minutes while using the device on your nightstand; or set it in your washroom vanity and/or kitchen counter as you begin your morning routine.

If you purchase a portable device, you can bring your unit to your workplace and position it on your desk, within 24 inches from where you sit (obviously this recommendation applies to those working in an office environment. These devices are not effective as “ambient light” – i.e., placed on the other side of the room as you go about your day). You can expose your self to bright (10’000 lux) white light for the day, but research suggests 30 to 60 minutes at least. My personal experience suggests between the hours of approximately 3:00 PM and 5:00 PM (the hours when in Toronto it begins to become perceptively darker), work well.

If you are considering a second, white light device for workplace use, here are two options that you might consider, a sleek, lower cost, option; and a slightly more expensive, adjustable light intensity option.

Lastly, there are obviously many other strategies that naturopathic medicine offers for management of Seasonal Affective Disorder (SAD), depression, anxiety and other mood disorders, that are outside the scope of a blog post, but if you are at the point you want to be aggressive about resolving your mood issues, get in touch.

Jonah Lusis, ND


  1. Thase ME. The new “blue light” intervention for seasonal affective disorder (SAD). Medscape [Internet]. [cited 2018 Dec 5]. Available at: https://www.medscape.org/viewarticle/550845?src=ppc_google_rsla_ed_ous_9mo&gclid=Cj0KCQiA6JjgBRDbARIsANfu58GtBXQyoQes-QHyfMws5tvmpq4UYR72kn4aVHKFIUgg_mPusQtl7q4aAnljEALw_wcB.
  2. Menculini G, Verdolini N, Murru A, Pacchiarotti I, Volpe U, Cervino A, et al. Depressive mood and circadian rhythms disturbances as outcomes of seasonal affective disorder treatment: A systematic review. J Affect Disord. 2018 Dec 1;241:608-626.
  3. Srinivasan V, Smits M, Spence W, Lowe AD, Kayumov L, Pandi-Perumal SR, et al. Melatonin in mood disorders. World J Biol Psychiatry. 2006;7(3):138-51.
  4. Sargis RM. An overview of the pineal gland: maintaining circadian rhythm. endocrine web [Internet]. [cited 2018 Dec 5]. Available at: https://www.endocrineweb.com/endocrinology/overview-pineal-gland.
  5. National Sleep Foundation [Internet]. Melatonin and sleep. [cited 2018 Dec 5]. Available at: https://www.sleepfoundation.org/sleep-topics/melatonin-and-sleep.
  6. Brainard GC, Hanifin JP, Greeson JM, Byrne BGlickman G, Gerner E, et al. Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor. J Neurosci 2001 Aug 15;21(16):6405-12. Available at: http://www.jneurosci.org/content/21/16/6405.long.
  7. Lighting Research Centre [Internet]. How valid are the claims regarding full-spectrum lighting sources? [cited 2018 Dec 5]. Available at: https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/fullspectrum/claims.asp.



Posted: 2018 Dec 6