Light Boxes for Winter Depression: What the Trials Support and How to Use One Well
Seasonal depression is more than winter blues. Here is what bright light trials show, how to use a light box, who should ask a doctor first, and a four-week mood log.
The clocks go back, and for a week or two the change feels almost pleasant, an extra hour in bed, a cosy excuse to stay in. Then one afternoon you look up from your desk and it is already dusk, and something in your chest goes quiet. Most of us call that the winter blues and wait for spring. For some people it is more than that, and the difference is worth knowing, because there is a treatment with decent evidence behind it that costs a one-time purchase and about half an hour a morning.
Seasonal affective disorder is not the same as winter blues
Winter blues are common and mild. You sleep a bit more, you want carbohydrates, you feel flatter than in July, and you still function. Seasonal affective disorder, usually shortened to SAD, is a form of depression that follows the calendar. The mood drop is heavy enough to interfere with work, relationships, or basic self-care, and it tends to return in the same season year after year, easing in spring.
The signs people describe are the ones you would expect from depression, with a winter flavour: low mood most of the day, loss of interest, heavy limbs, oversleeping, cravings, difficulty concentrating, a sense of dread about the months ahead. A clinician will usually want to see the seasonal pattern over more than one winter before naming it. That is one reason to talk to a professional rather than self-diagnose from an article, including this one.
If you ever notice thoughts of harming yourself, that is not a light-box situation. In the US you can call or text 988 at any hour, and a doctor's appointment should be made that day.
What the trials actually support
The evidence for bright light therapy is better than for most home remedies, and also more modest than the marketing. A systematic review and meta-analysis from Taipei Medical University, pooling randomized and crossover trials, found that bright light therapy reduced SAD symptoms at two weeks, with less clear effects at other time points. A network meta-analysis published in 2025, which compares several treatments at once, ranked white light highest among the light options it examined.
I would hold both findings loosely. I am describing them in broad strokes, and the exact effect sizes belong in the original papers, which are worth reading yourself before you quote a number to anyone. Light-therapy trials have a hard design problem: it is difficult to blind people to a very bright lamp, so some of the benefit may be expectation. And "less clear at other time points" is an honest phrase. It does not say the treatment stops working, it says the data are thinner or messier past the two-week mark.
What I take from the whole picture is this. For people whose depression follows the dark months, a properly used light box is a reasonable first thing to try, it is low-risk for most people, and it should be judged by your own mood log over a few weeks, not by a promise on a box.
How a light box is meant to be used
Four variables matter, and the instructions that come with a reputable device will state them. The figures below are the commonly cited ranges, so treat your device's manual and your clinician as the final word.
- Intensity. The usual target is about 10,000 lux of white light at the distance the manufacturer specifies. A lamp that is rated 10,000 lux at 6 inches is not delivering that at arm's length. Check the distance on the label, not just the headline number. Choose a device that filters out UV.
- Distance. Close enough to hit the stated intensity, usually somewhere between about 16 and 24 inches for the larger boxes. Set it a little above or to the side of your eye line, rather than straight ahead, so the light reaches your eyes without you having to stare into it.
- Timing. Morning, ideally soon after you wake. Light late in the evening can delay your body clock and make sleep worse, which defeats the purpose.
- Duration. Commonly 20 to 30 minutes at 10,000 lux. Weaker lamps need longer. Many people start with a shorter session and build up if they feel jittery.
Your eyes should be open, but you do not need to look at the lamp. Reading, eating breakfast, or answering email next to it works fine. That is the quiet advantage of the morning routine: it can be attached to something you already do. For me, the habits that survive are the ones that ride along on another one, like a coffee or a commute.
Some people notice mild headache, eyestrain, nausea, or an edgy, wired feeling in the first days. Moving the lamp slightly farther away or shortening the session often settles it. If it does not, stop and ask.
Who should check with a doctor first
Light is a real intervention, which is exactly why it is worth a short conversation for some people.
- Bipolar disorder. Bright light can, in some people, tip mood toward mania or hypomania. If you have a bipolar diagnosis, do not start a light box on your own.
- Eye conditions. Retinal disease, macular degeneration, glaucoma, cataracts, and eye complications of diabetes are all reasons to have an eye doctor weigh in first.
- Photosensitizing medicines. Some antibiotics, some psychiatric medicines, and the herbal supplement St John's wort can make skin or eyes more sensitive to light. Ask your pharmacist to check your list.
- Photosensitive skin or a history of skin cancer. Reputable boxes filter UV, but this is still worth mentioning.
A pharmacist can answer the medication question in a few minutes, usually at no charge. If you are unsure whether any of this applies, that uncertainty is itself the reason to ask.
Where light sits next to therapy and medication
Light is not a rival to the other treatments, it is one option on the same shelf. Cognitive behavioural therapy adapted for SAD is well studied and has a feature the lamp does not: people who learn the skills tend to keep them, and that may matter in the next winter. Antidepressants are another established option, and some people use a medicine and a lamp together.
The sensible way to think about it is by severity. For mild-to-moderate seasonal low mood, light on its own is a fair place to begin. For something heavier, or for anyone who has been unable to function, light is something to discuss as part of a plan with a clinician, not a substitute for one. And outdoors counts too. A walk in the morning daylight, even on a grey day, is brighter than most indoor rooms, which is a point in its favour that no product can claim.
A four-week setup checklist and mood log
The point of a trial period is to find out whether this works for you, so write things down. Memory in winter is unreliable on exactly this question.
Before you start (a few days ahead)
- Read the device manual and note its stated lux and distance.
- Check the box on the "who should check first" list above. If anything applies, ask your doctor or pharmacist first.
- Choose the spot and the anchor habit, such as breakfast or the first email check.
- Write your baseline: mood, energy, and sleep over the past week, each out of 10.
Week 1. Ten to fifteen minutes each morning at the right distance. Note any headache, eyestrain, or jitteriness. Adjust distance or time if needed.
Week 2. Build to the full 20 to 30 minutes if you are comfortable. Keep the same time each day. This is the point in the trials where effects looked clearest, so pay attention to your log.
Week 3. Hold steady. Look at the log. Has anything moved, even slightly: waking, energy at 3 pm, interest in things? Do not change several variables at once.
Week 4. Compare your week-4 numbers to your baseline. If there is a clear improvement, keep going through the winter. If there is none, that is useful information too, and a good moment to talk to a doctor about the next step, not to push harder alone.
Daily mood log (two minutes, same time each evening)
| Date | Mood /10 | Energy /10 | Bedtime and wake time | Light session (minutes) | Side effects | One-line note |
|---|---|---|---|---|---|---|
Copy that into a notebook or a spreadsheet and carry it through the month. A mood that slides lower on the log despite the lamp is worth a call to your doctor sooner, not later.
FAQ
Can I just use a bright desk lamp or my phone screen?
Not really. Ordinary lamps and phone screens are far dimmer than a light box rated for 10,000 lux, and the trials used proper devices. A bright morning outdoors is a better free substitute than a screen.
When should I start in the season?
Many clinicians suggest starting in early autumn, before symptoms build, if you know your pattern. If you are already low, starting now is still reasonable, once you have checked the safety list.
Is it safe for my eyes?
For most people with healthy eyes, a UV-filtered box used as directed is considered low-risk. Anyone with an eye condition, or taking a photosensitizing medicine, should check with a doctor first.
How long until I know if it works?
Some people feel a change within a week or two, others need longer. Four weeks of consistent use plus a written log is a fair test. If nothing has shifted, speak to a clinician about other options.
Can I use light therapy and still take medication or see a therapist?
Yes, many people do. Tell whoever prescribes or treats you that you are adding a light box, so they can see the whole picture.