A light therapy lamp works through your eyes, not your skin. Bright light reaching the retina is picked up by specialised cells that signal the brain's master clock, and a strong dose of light soon after waking tells your body that the day has started. That is the short answer to "how does a light therapy lamp work?". The longer answer covers why the lamp has to be so bright, why distance is part of the specification, why morning is the usual time and why it makes no vitamin D.
What happens when bright light reaches your eyes?
Your body runs on a circadian rhythm: a roughly 24-hour internal cycle that sets when you feel alert, when you feel sleepy and when hormones rise and fall. It is kept in time mainly by light.
The retina at the back of each eye contains a small population of specialised cells, intrinsically photosensitive retinal ganglion cells, which hold a light-sensitive pigment called melanopsin. They are not there to help you see. They measure how bright the world is and report to the suprachiasmatic nucleus, the master clock in the brain.
When these cells register bright light, the clock takes it as a marker of daytime. Dim light, of the kind most homes have at 7am in January, barely registers. Our introduction to light and your daily rhythm covers this in more detail.
Why does the time of day matter so much?
Light does not just tell the clock that it is day; it nudges the clock's timing. Bright light in the morning tends to shift the body clock earlier, so you feel sleepy a little earlier that evening and wake more readily the next day. Bright light late in the evening tends to shift it later.
Light also suppresses melatonin, the hormone your body releases in the evening and overnight as part of preparing for sleep, for as long as you are exposed to it. In the morning that is helpful: the night-time signal is being switched off. Late at night it is the opposite of what you want.
This is why a light therapy lamp is used soon after waking. The same lamp, switched on at 10pm, could push your sleep later.
How much brighter is a lamp than normal indoor light?
Lux is the unit for how much light falls on a surface, such as your face. The figures below are approximate, but the gap between indoors and outdoors is the point.
| Situation | Approximate light level |
|---|---|
| Bright midsummer sunshine | 50,000–100,000 lux |
| Overcast UK winter day, outdoors | 1,000–5,000 lux |
| Light therapy lamp at its rated distance | 10,000 lux |
| Bright office | 300–500 lux |
| Living room in the evening | 50–150 lux |
A well-lit kitchen on a winter morning gives your eyes a few hundred lux; a lamp at its rated distance gives 20 to 30 times more. Your eyes adapt so quickly that indoor light feels perfectly bright, but to the clock it is closer to dusk than to daylight.
Why is 10,000 lux at a stated distance the standard?
Light boxes are often called SAD lamps after seasonal affective disorder (SAD), a form of depression that follows a seasonal pattern and is usually worse in winter. The NHS describes light therapy as using a bright light to simulate daylight in winter, with 10,000 lux as the standard. A 2020 meta-analysis of 19 randomised trials by Pjrek and colleagues found bright light therapy modestly better than dim-light placebo for SAD, with caveats about study size and quality.
A lamp only delivers its rated figure at one distance, so a lux number without a distance tells you little. Move further away and the light reaching your eyes falls quickly; our post on what 10,000 lux actually means shows how quickly.
This is why we state both numbers. DAYARC Rise is rated at 10,000 lux at approximately 30–36 cm, a normal distance from your face to a lamp beside a breakfast plate. DAYARC Mini is rated at 10,000 lux at approximately 25 cm, so it needs you a little closer. Both are UV-free LED, which is what the NHS advises looking for, and we describe them by their specifications rather than by promises.
Do you have to look at the lamp?
No, and you should not stare at it. Your eyes must be open and the panel within your field of view, but you do not look into it. Place the lamp slightly to one side and a little above eye level, angled towards your face, then read, eat or work as normal. Glancing towards it now and then is enough.
Two things set the dose: distance and duration. At the rated distance, a session of around 20–30 minutes soon after waking is a common starting point; sit further away and you need longer. Mini's guidance makes this explicit: about 25 cm for 30 minutes, roughly 35 cm for 60 minutes, roughly 50 cm for 120 minutes. Our guide to how far to sit from a light therapy lamp covers measuring and marking the spot.
It is also about the eyes, not the skin. Light on your arms or the back of your neck does not reach the cells that matter, which is why the panel sits in front of you.
What does a light therapy lamp not do?
- It does not make vitamin D. Your body makes vitamin D when UVB from sunlight reaches the skin, and Rise and Mini are UV-free, so they cannot. The NHS notes that in the UK we do not make enough vitamin D from sunlight between October and early March, and suggests adults consider a daily 10 microgram supplement in autumn and winter.
- It does not tan. No UV means no tan.
- It does not wake you up. Neither DAYARC lamp is a sunrise alarm clock. You switch it on after you wake.
- It is not red light. Red light devices are aimed at the skin; a bright-light lamp is white light aimed at the eyes.
- It is not a treatment. The NHS notes that light therapy is not usually available on the NHS because there is not enough evidence to tell whether it is effective, and lists talking therapies such as CBT and antidepressants as treatments for SAD. A lamp can support a morning routine; it is not a substitute for seeing a GP.
Frequently asked questions
Do you have to look directly at a SAD lamp?
No. Keep your eyes open and the panel within your field of view, slightly to one side and angled towards you. Staring into it is uncomfortable and unnecessary.
Does a light therapy lamp work with your eyes closed?
Generally no. The cells that signal the body clock are in the retina, and closed eyelids block most of the light. Dozing in front of the lamp is not a session.
Can I wear glasses while using a light therapy lamp?
Clear prescription glasses and clear contact lenses are fine. Tinted, photochromic or blue-blocking lenses cut out part of the light the clock responds to, so take them off for the session if you can.
Does daylight through a window count?
Partly. Daylight through glass is often far brighter than the room, but it varies with the weather, the season and which way the window faces. Our post on morning light through a window looks at when it is enough.
Where does this leave you?
If the mechanism makes sense, the checklist is short: a lamp that delivers 10,000 lux at a distance you can actually sit at, in your field of view, soon after waking, most days through the darker months. DAYARC Rise is built for a regular place at home, with four settings, a timer and an adjustable stand. DAYARC Mini is the compact option for smaller spaces and mornings away. The routine matters more than the choice.
About DAYARC
DAYARC is a new UK circadian rhythm startup. We make two bright-light lamps for the morning: DAYARC Rise (£199), a full-size lamp rated at 10,000 lux at approximately 30–36 cm, with four brightness settings, a 15 to 60-minute timer and adjustable height and angle; and DAYARC Mini (£49.99), a compact lamp rated at 10,000 lux at approximately 25 cm, with a folding stand that doubles as its cover. Both use UV-free LEDs and run from the mains. We publish plain specifications with the measuring distance, we do not make medical claims, and we write the DAYARC Journal to help people build a simple morning light routine around their own daily rhythm. Both lamps are in stock in the UK and dispatched within 2 working days. You can read more about how we think on our approach page or compare the two lamps.
This article is general information, not medical advice. Check with a GP or qualified healthcare professional before using bright light if you have an eye condition, a condition affected by bright light such as bipolar disorder, or take medicines that increase sensitivity to light. If you have persistent low mood or think you may have depression, speak to your GP. If you or someone else is in crisis, call NHS 111 or, in an emergency, 999.