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Light therapy: the dose that works

10 000 lux for 30 minutes in the morning — the dose the trials actually used, and how to deliver it.

This is seasonal self-care information, not a diagnosis and not treatment advice. Seasonal affective disorder is a clinical diagnosis made by a clinician; bright-light therapy is not safe to self-start for everyone (bipolar disorder and some eye conditions come first); and any measured vitamin D deficiency is treated at a clinician's dose, not a supplement-shelf one. If thoughts of self-harm are present, the step is crisis services now — the <a href="/therapists">mental health page</a> carries the national crisis lines.

What the evidence used

The controlled trials of bright light for winter depression standardised on about 10 000 lux at eye level for 30 minutes, taken in the morning. Lux is the light falling on a surface, not a property of the lamp — the same box produces 10 000 lux at 40 cm and a quarter of that at 80 — so the distance is part of the dose. A 10 000-lux box used at arm's length for half an hour is the reference treatment; used across the room it is a reading lamp.

Timing

Morning light is the treatment because it is the morning signal: light around waking advances the circadian clock and suppresses the melatonin that should have stopped. The same light in the evening delays the clock and pushes sleep later, which is the opposite of what a winter morning needs. The practical rule is light in the first hour or two after waking, and dim light — screens included — for the last hour before bed.

What to expect

Response is usually felt within a week or two when it comes at all, and it tends to be modest: the effect sizes in the trials are real but not dramatic, which is why the honest framing is a useful tool rather than a cure. Headache and eye strain happen at the start for some people; shortening the session and increasing the distance, then building back up, is the standard fix. People with bipolar disorder or an eye condition should not start bright-light treatment without asking a clinician, because light can trigger mania in the former and is a strain on the latter.

Choosing a box

The numbers that matter: at least 10 000 lux at the distance you will actually use it, UV-free (the box should state it — a therapy box is not a tanning lamp), a screen large enough that you do not have to hold still at an exact distance, and a price that reflects a plastic box with LEDs rather than anything medical. Wake-up lights and dawn simulators are a different category: pleasant, useful for waking, but far below the lux dose the therapy trials used, and not interchangeable with a light box.

Light therapy dosing: the bright-light trials (10 000 lux, 30 minutes, morning). Vitamin D: the Nordic national nutrition recommendations. Circadian facts: the standard chronobiology literature (melanopic response, dim-light melatonin onset). The depression line: clinical diagnostic practice — seasonal affective disorder is diagnosed by a clinician. Checked 2026-09-06.

Frequently asked questions

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