Seasonal affective disorder (SAD) is a form of recurrent depression or bipolar disorder that comes and goes at certain times of the year.1 The most common type is the winter form W-SAD, colloquially called “winter blues”. SAD affects around 2.4% of people in Austria and tends to increase towards the north.1 In Finland, 9.5% of the rural population fulfills the criteria of winter SAD and 18.5% a sub-syndromal form of it.2 In a survey in Germany, a little less than a third stated an impaired mood during winter times.3

SAD is associated with a delayed circadian phase. People with delayed sleep phase syndrome (DSPS) are 3.3 time more likely to have SAD.4 It severity correlates with the magnitude of the delay.

Bright light therapy

Bright light therapy (BLT) is the treatment of first choice for seasonal affective disorder. The recommended setting is an exposure to 7000-10000 lux of broad spectrum white light for 30 minutes each morning for at least 2 weeks. If natural daylight is not available, the typical light source is a daylight lamp, but light therapy glasses are an emerging alternative. The exact timing depends on the individual chronotype and should be assessed together with a physician. BLT can improve symptoms of SAD already after a couple of days and is most effective when performed consistently each day at the same time. 5

Light is thought positively influence mood via two ways:

  •  The consistent exposure stabilizes and amplifies circadian rhythm. The synchronization between circadian clock and external schedule appears to be beneficial, as BLT in the morning has been shown to be more efficient than BLT at other times of the day5.
  • Light modulates the availability of serotonin and other monoamines, which are a critical factor in affective disorders and sleep regulation5.

The exact mechanics behind BLT are still an active field of research.

Dawn simulation

Artificial dawn has also been shown to be an effective counter-measure against SAD. Dawn simulation lighting starts about 90 minutes before scheduled awakening at very low intensitiy (0.001 lux) and then slowly increases to a maximum of ~300 lux until scheduled wake time5. In a study, dawn simulation has been able to improve symptoms of SAD by 49.5%, while BLT improved symptoms by 57.1%6. As many people find it difficult to stick to a given early-morning BLT schedule7, dawn simulation may be an attractive alternative.
The caveat here is that the light sources used in the studies had a diffuse, wide lighting area, providing a proper illumination independent of people’s sleeping position. This is not the case for commercial wake up lights and their small luminous field. Therefore, dawn simulation with commercial wake up lights is not an officially recommended treatment for SAD5.


The lack of sunlight during winter can pose a serious threat to your mood. This winter blues appears to be linked to a delayed circadian phase. Applications of light in the morning have the potential to cure or alleviate seasonal affective conditions. They come in the form of bright light therapy as the treatment of first choice as well as dawn simulation as a possible alternative.

If you find yourself suffering under SAD, please seek professional medical help. If you plan to incorporate light therapy into your morning routine, you can find information on how to choose suitable devices in our articles on daylight lamps and light therapy glasses.


[1] Pjrek, E., Baldinger-Melich, P., Spies, M., Papageorgiou, K., Kasper, S., & Winkler, D. (2016). Epidemiology and socioeconomic impact of seasonal affective disorder in Austria. European Psychiatry32, 28–33.

[2] Saarijärvi, S., Lauerma, H., Helenius, H., & Saarilehto, S. (1999). Seasonal affective disorders among rural Finns and Lapps. Acta Psychiatrica Scandinavica, 99(2), 95–101.

[3], accessed on 2021/01/24

[4] Lee, H. J., Rex, K. M., Nievergelt, C. M., Kelsoe, J. R., & Kripke, D. F. (2011). Delayed sleep phase syndrome is related to seasonal affective disorder. Journal of Affective Disorders, 133(3), 573–579.

[5] Wirz-Justice, A., & Bromundt, V. (2013). Lichttherapie. Schlaf, 2(01), 20-29.

[6] Terman, M., & Terman, J. S. (2006). Controlled trial of naturalistic dawn simulation and negative air ionization for seasonal affective disorder. American Journal of Psychiatry, 163(12), 2126–2133.

[7] Oren, D. A., Shannon, N. J., Carpenter, C. J., & Rosenthal, N. E. (1991). Usage patterns of phototherapy in seasonal affective disorder. Comprehensive Psychiatry, 32(2), 147–152.