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Even in the pre-COVID times, the pervasive grey of winter could leave a person feeling down. As the days grow shorter and the nights longer, getting out of bed can become more difficult and motivation can seem fleeting.
It’s not just the laziness that comes with wearing sweats all day—the winter blues are real. Seasonal affective disorder (SAD) is a form of depression that about one in 20 Americans experience during the shortest, coldest months. And though researchers aren’t exactly sure of the mechanisms that cause SAD, we understand enough to have developed an effective treatment: light therapy, a.k.a. happy lamps.
The science behind these fancy light fixtures is even more simple than you might think—and it’s surprisingly effective.
What is SAD?
Seasonal affective disorder is triggered by a change in seasons. The most cases manifest in the change from autumn into winter. Summer to autumn SAD, or “summer depression,” does affect some people, although it’s less common than winter SAD. It can manifest as simply the winter blues in mild cases, but it can also be a form of depression.
Symptoms of the more extreme versions include sadness, anxiety, extreme fatigue and an inability to concentrate, among others. Other conditions can make a person more susceptible to SAD, including mood disorders like bipolar disorder. Then there are geographic and environmental factors, like living far north or south of the equator, which means receiving significantly less sunlight during the short days of winter.
How does SAD work?
Although the specific cause is unknown, researchers have narrowed the search to a handful of factors, the most prominent based on the general lack of sunlight during the winter months.
The gradual shortening of days until the winter solstice messes up our circadian rhythm, the biological clock that takes note of daylight hours and regulates sleep, appetite, body temperature, heart rate and hormone production.
In the daytime, light enters the retina and stimulates the hypothalamus, the part of the brain that maintains circadian rhythms, letting the body know it’s time to be awake and functioning. On the flip side, the production of melatonin, a brain hormone that regulates sleep, is triggered when the body is in darkness. High levels of melatonin tell the body it’s time to go to sleep. But the dark mornings and early nightfall of winter can interfere with the timing of its production, and can lead to fatigue during the day and disruptions to the normal sleep cycle at night.
When sunlight goes away, it can also take serotonin away with it. Serotonin is known as the “happy hormone,” as it regulates mood, body temperature and appetite. A severe drop in serotonin might activate the effects of depression in SAD during the winter months.
When sunlight becomes harder to come by, it can send the body into a tailspin that’s hard to correct and manifests in SAD.
How can light therapy help SAD?
The goal of light therapy is to correct the disruption to the body’s internal clock brought on by the changing seasons. Happy lamps are designed to imitate natural sunlight and correct disturbances to the circadian rhythm. In the morning hours, these lamps bring the sunlight that’s missing from the outside world indoors to let the body know it’s daytime and ensure its internal clock is set correctly.
The light emitted enters the eyes and stimulates the retina, activating the hypothalamus and calibrating the body’s clock to daytime. To have this effect, the lamp must trick the body into thinking it’s the morning sun. Specialized light boxes are designed to give off intense light over a flat surface to achieve this imitation. Typical household lamps have too narrow a beam and too low an intensity to achieve the same effect.
While happy lamps mimic the sun’s intensity, they do not emit UV light nor do they provide vitamin D. UV light therapy is a separate treatment for certain skin conditions, but not for SAD.
Medical researchers consider light therapy to be generally effective, with some variation from person to person. Studies have shown that light therapy can be just as effective as prescription antidepressants and mental health counseling. Keep in mind, though, that light therapy does not cure SAD, but alleviates symptoms.
Light therapy can also be used to reset the circadian rhythm after disruptions unrelated to the seasons. It’s a supplemental treatment for sleep disorders, as well as a tool for recovering from jet lag.
How to use a happy lamp
Light therapy for SAD is most effective when you start using the lamp in the early fall and continue on until spring, when enough ambient daylight is restored and symptoms subside. Consistent, daily sessions are key for setting and reinforcing an artificial circadian rhythm that lasts the whole season.
Before going all-in on a quality light box, there’s a variety of features and options to consider for meeting your needs. According to the Mayo Clinic, there are three key elements to keep in mind for maximum effectiveness: intensity of light, duration of exposure, and timing of exposure.
The intensity of light is measured in lux, a unit that represents the light output per square meter of surface. Most indoor lighting maintains an intensity between 50 and 500 lux. Ambient daylight falls in the range of 10,000 to 25,000 lux, so the recommended intensity for SAD light therapy is at least 10,000 lux.
The duration of exposure varies depending on the intensity of the light. For a 10,000-lux lamp, a 20 to 30 minute session every morning will do the trick, but longer may be needed for lamps with lower intensity. Be sure to follow the manufacturer’s guidelines for your specific lamp.
Finally, the light must indirectly enter your eyes in order to do its job properly. Position the lightbox two to three feet away from your face (though don’t look straight at it!). The therapy is also most effective if you do it when you first wake up, so set up your happy lamp while you have a cup of coffee, eat breakfast, or read the morning newspaper. Consistency is key, so make a schedule and stick to it.
Correction 3/15/21: An error was introduced in edits that mistakenly stated the hippocampus helped calibrate the body’s clock to daytime. In fact it is the hypothalamus.