Every fourth quarter, several million people in the UK buy a light box hoping it will lift the fog of a dark winter, use it a handful of times, and quietly give up. The lamp usually isn’t the problem. How it’s used almost always is. Getting a genuine benefit from light therapy for seasonal affective disorder (SAD) depends on three variables working together — light intensity, distance from the device, and timing — and the box on a shop shelf tells you almost nothing about any of them. This is a consumer-protection question as much as a health one: understand the mechanism and a lamp you already own may start working; skip it and a well-made box does nothing more than a bedside light.
Lux is the number that actually matters
The output level that clinical use is built around is 10,000 lux — roughly twenty times the brightness of typical indoor room lighting. This is the figure behind most published light-therapy protocols, and it’s why a lamp marketed for SAD needs to be judged on its lux rating at a stated distance, not on wattage or general brightness claims. If a device only reaches a lower intensity, such as 2,500 lux, the shortfall isn’t fatal, but the exposure time has to increase substantially — up to around two hours a day — to get an equivalent effect. That trade-off is worth knowing before you buy: a smaller, dimmer lamp may look more convenient, but it can quietly demand an amount of daily time that nobody actually sticks to.
Distance: close enough, not eyes-on
Lux output falls away sharply with distance, so the manufacturer’s stated distance is not a suggestion — it’s the only way the rated lux reaches you at all. As a general guide, most 10,000 lux boxes need to sit around 40 to 60cm (roughly 16 to 24 inches) from your face to deliver that intensity, though this varies by model and some compact lamps require sitting notably closer. Sit further back than that to feel more comfortable and the effective lux at your eyes drops well below the number on the box, even though the lamp itself is working exactly as designed. You don’t need to stare into the light for it to work: the light needs to reach your eyes indirectly, so reading, eating breakfast or working at a laptop in front of it is the normal way to use one. What does undermine it is wearing tinted lenses, dark glasses, or blue-light-blocking glasses during the session — any of these can meaningfully reduce the light actually reaching your retina.
Timing is not optional
Light therapy works by helping reset the body’s internal clock, and that only happens reliably if it’s used at a consistent time, in the morning. The general guidance is to use the lamp within an hour of waking, broadly within a six-to-nine-a.m. window, every day including weekends, for as long as symptoms are present — typically from when they start in autumn through to spring. Evening use is the one timing mistake that can actively work against you: bright light late in the day can push your body clock in the wrong direction and disrupt sleep, which is precisely the outcome someone using a lamp for low winter mood is trying to avoid.
Where people go wrong
- Using it for ten minutes instead of twenty to thirty. Most guidance centres on 20–30 minutes daily at 10,000 lux (some protocols run 30–60 minutes); a quick five-minute burst before rushing out the door rarely reaches a therapeutic dose.
- Sitting further back than the manufacturer specifies, for comfort. This defeats the lux calculation the whole session depends on.
- Using it in the evening because mornings are too rushed. Wrong time of day can work against sleep rather than helping mood.
- Giving up after a week with no obvious change. Consistency day after day is part of how the effect builds; sporadic use rarely shows a clear result either way.
- Assuming any bright lamp will do. A desk lamp or daylight bulb is not calibrated or lux-rated for this purpose, however bright it looks.
SAD lamp or dawn simulator — they are not interchangeable
The two devices are often shelved together but do different jobs. A standard SAD lamp delivers a high, steady dose of light — typically the full 10,000 lux — for a fixed session once you’re already awake. A dawn simulator instead gradually brightens over a period before your alarm, mimicking a sunrise, and generally does not reach anywhere near 10,000 lux. Some research suggests dawn simulators can be comparably effective for people who find a full-intensity light box too harsh or who struggle simply to get out of bed in the dark, and the two can be used together rather than as strict alternatives.
| Feature | SAD lamp (light box) | Dawn simulator |
|---|---|---|
| Typical output | ~10,000 lux | Well below 10,000 lux |
| How it’s used | Fixed session, sit at a set distance | Runs automatically before your wake time |
| Session length | 20–30 minutes, once awake | Gradual rise over 20–30 minutes pre-alarm |
| Best suited to | Those wanting a concentrated, measurable dose | Those who find bright light boxes harsh or hard to fit in |
The consumer-choice point
None of this is complicated once it’s laid out, but it’s rarely printed clearly on the packaging of the lamp itself, which tends to sell on brightness and design rather than on the protocol that makes the brightness useful. Understanding the lux, the distance and the timing turns light therapy from a guess into something you can actually evaluate for yourself — keep a simple note of when and how long you use it and whether your mood or energy shifts over a couple of weeks. That’s the same instinct this site has always argued for: know what you’re using and why, rather than trusting a claim on a box, before you decide whether it’s worth your money or your morning.