A standard light therapy session lasts 30 minutes per day when using a 10,000 lux lamp. That’s the duration backed by the most clinical evidence, particularly for seasonal affective disorder (SAD). But the right session length for you depends on your lamp’s brightness, how far you sit from it, and what you’re using it for.
The 30-Minute Standard at 10,000 Lux
Research from Yale School of Medicine found that 30 minutes of exposure at 10,000 lux, seven days a week before 8 a.m., produces substantial improvement in SAD and milder winter depression for most people. This has become the go-to recommendation across most clinical guidelines. The American Academy of Family Physicians puts the effective range at 30 to 60 minutes daily, depending on the device and individual response.
If your lamp is lower intensity, you’ll need longer sessions. A 2,500 lux device, for example, requires roughly two hours to deliver a comparable dose. That’s why most experts recommend buying a 10,000 lux lamp: the shorter session is far easier to stick with day after day.
How Distance Changes Your Session Time
The brightness reaching your eyes drops significantly the farther you sit from the lamp. A light box rated at 10,000 lux typically achieves that intensity at a specific distance, often around 16 to 24 inches. Move further back and the effective lux drops, meaning you’d need a longer session to get the same benefit.
Think of distance and time as two sides of the same equation. If you double your distance from the lamp, the light energy reaching you can drop by more than half, and your session time needs to increase proportionally. The practical approach: position yourself at the distance your manufacturer recommends first, then set your timer. Don’t try to compensate for poor positioning by simply sitting longer.
Best Time of Day for Sessions
Morning sessions, shortly after waking, are the most effective for both mood and sleep-related uses. For SAD, the Yale recommendation specifically calls for sessions before 8 a.m. For people with delayed sleep patterns (difficulty falling asleep and waking up), Stanford Health Care recommends light exposure as soon after natural waking as possible.
The reason is biological. Morning bright light shifts your internal clock earlier, suppressing the sleep hormone melatonin at the right time and reinforcing your natural wake-up signal. Evening sessions can actually backfire, making insomnia worse by pushing your clock in the wrong direction. Some people also find success with dawn-simulation lights that turn on gradually before their alarm, though these are a different approach from a standard light box.
How Long Before You Feel a Difference
Most people with SAD notice improvement within one to two weeks of consistent daily use. Some respond faster, within just a few days, while others need three to four weeks to feel a meaningful shift in energy and mood. The key variable is consistency. Skipping days or varying your timing significantly slows the response.
If you’ve used your lamp daily for three to four weeks with no improvement, the issue may be your lamp’s actual lux output, your positioning, or the timing of your sessions rather than light therapy itself not working for you.
How Long to Keep Using It
For seasonal depression, light therapy is typically a full-season commitment. Most people begin sessions in early fall when daylight shortens and continue through spring. Stopping too early, even if you feel better, often leads to symptoms returning within a few days to a couple of weeks.
Once your symptoms have been stable for a while, you can experiment with shorter sessions. Stanford Health Care notes that after reaching a desired sleep schedule, patients can reduce their session duration while maintaining a consistent morning routine. Some people find that 15 to 20 minutes is enough for maintenance, while others need the full 30 minutes throughout the season. Keeping a fixed wake time, even on weekends, helps sustain the benefits.
Signs You’re Overdoing It
More is not better with light therapy. Sessions longer than 60 minutes at high lux haven’t shown additional benefit for mood disorders, and they can cause side effects. The most common signs of overexposure include headaches, eye strain, a jittery or agitated feeling, and occasionally mild nausea or fatigue.
If you experience any of these, try cutting your session shorter by 10 minutes or moving slightly further from the lamp. These symptoms typically resolve quickly once you adjust. People with bipolar disorder should be particularly cautious, as bright light therapy can sometimes trigger a shift toward elevated mood states. Starting with shorter sessions of 15 minutes and increasing gradually gives you a safer window to monitor your response.
Quick Reference by Lamp Intensity
- 10,000 lux: 30 minutes per day, seated 16 to 24 inches from the lamp
- 5,000 lux: approximately 60 minutes per day
- 2,500 lux: approximately 2 hours per day
These times assume you’re at the manufacturer’s recommended distance. Always check your specific device’s instructions, since lux ratings are measured at a fixed distance that varies between products. A lamp marketed as 10,000 lux may only deliver that intensity at 6 inches, making it functionally much dimmer at a comfortable sitting distance.