Every year around October, the same thing happens. The days get shorter, the skies turn grey, and something shifts. Maybe you feel a bit slower. Less motivated. More drawn to the couch than to your friends. You tell yourself it's just the weather, that everyone feels this way.
But what if it's something more — and more importantly, something treatable?
What SAD Really Is
Seasonal Affective Disorder (SAD) isn't just a case of feeling a bit down when it's cold outside. It's a clinical form of depression that follows a seasonal pattern, typically emerging in late autumn and lifting in spring. The symptoms can be significant:
- Persistent low mood and lack of interest in activities
- Low energy and difficulty concentrating
- Changes in appetite, often craving carbohydrates
- Sleeping more than usual but still feeling tired
- Social withdrawal and irritability
The condition affects an estimated 5-10% of the population in northern latitudes, with women being diagnosed more frequently than men. In Scandinavia, where winter days can offer just a few hours of weak sunlight, these numbers are even higher.
Why It Happens: The Light Connection
The root cause of SAD lies in something remarkably simple: light. Or rather, the lack of it.
Our bodies run on an internal clock — the circadian rhythm — that regulates everything from when we feel sleepy to when hormones are released. This clock is primarily set by light entering our eyes, particularly bright light in the morning.
When winter arrives and daylight becomes scarce, several things go wrong:
The suprachiasmatic nucleus (SCN), our master clock in the brain, doesn't receive enough light signals to keep our rhythm properly synchronized. Melatonin, the hormone that makes us sleepy, may be produced at the wrong times. Serotonin levels, which affect mood, tend to drop when we're light-deprived.
For most of human history, this wasn't a problem. Our ancestors spent their days outdoors, receiving thousands of lux of natural light even on overcast winter days. Today, we spend 90% of our time indoors under artificial lighting that provides perhaps 100-500 lux — about 100 times dimmer than what our biology expects.
The Treatment That Works
Here's the good news: if lack of light causes the problem, adding light can solve it.
Bright light therapy has been studied for over 30 years and is now considered a first-line treatment for SAD by medical organizations worldwide. Some studies have shown it to be as effective as antidepressant medication for seasonal depression, with faster onset of action and fewer side effects.
The protocol is straightforward. Use a light therapy box that delivers 10,000 lux at your eyes. Sit in front of it for 20-30 minutes each morning, ideally within an hour of waking. You don't need to stare directly at it — most people read, eat breakfast, or work while receiving treatment.
The key factors that make light therapy effective:
Intensity matters. Standard indoor lighting is far too dim. You need 10,000 lux to trigger the biological response. This is why a purpose-built light therapy box works, while simply turning on more lamps doesn't.
Timing matters. Morning use is most effective because it helps shift your circadian rhythm earlier, counteracting the tendency to fall out of sync during winter. Evening use can actually make things worse by delaying your internal clock further.
Consistency matters. Like any treatment, light therapy works best when used regularly throughout the dark months. Most people notice improvement within a few days to two weeks.
What Light Therapy Doesn't Need
There's a common misconception that you need UV light for SAD treatment. You don't — and you shouldn't seek it out. Effective light therapy boxes are UV-filtered to protect your eyes and skin. The therapeutic wavelengths are in the visible spectrum, particularly the blue-green range that our circadian system is most sensitive to.
Similarly, you don't need to spend large amounts on therapy. While quality matters — look for devices that are flicker-free and genuinely deliver 10,000 lux at a reasonable distance — the technology itself is not complex. What you're paying for is consistent, bright, safe light.
Beyond the Light Box
Light therapy boxes are the most practical solution for most people, but they're part of a bigger picture. Supporting your body's light environment throughout winter can amplify the benefits:
Get outside when you can. Even on an overcast day, outdoor light is significantly brighter than indoor lighting. A 20-minute walk at lunch provides valuable light exposure.
Consider your indoor lighting. Many people benefit from brighter, cooler-temperature lighting during the day to maintain alertness, then transitioning to warm, dim lighting in the evening to support natural melatonin production.
Pay attention to morning routines. Opening curtains immediately upon waking, eating breakfast near a window, or using a dawn simulator alarm clock can all help reinforce your circadian rhythm.
When to Take It Seriously
If what you've read resonates with you, consider tracking your mood across seasons. Many people dismiss their winter low periods as normal or push through them with willpower. But if the pattern repeats year after year, and if it's affecting your relationships, work, or quality of life, you're dealing with something real — and something fixable.
SAD is one of the most treatable forms of depression precisely because we understand its cause so well. The light that's missing can be replaced. The rhythm that's disrupted can be reset.
This winter doesn't have to feel the same as the last.