They are answers to two different problems. The NHS says everyone in the UK should consider a daily 10 microgram vitamin D supplement from about October to early March, because winter sunlight here is too weak for skin to make enough; a SAD lamp does nothing for vitamin D at all, because it is UV-free by design, but it can give your body clock the bright morning signal that winter daylight fails to provide. Many people sensibly do both; neither replaces the other.
Why does the NHS recommend vitamin D in winter?
Skin makes vitamin D when it is exposed to the ultraviolet B part of sunlight. In the UK the sun is too low in the sky for that between October and early March, and the NHS says plainly that during those months we do not make enough from sunlight. Food alone rarely covers the gap, so the advice is that everyone, including pregnant and breastfeeding women, should consider taking a daily supplement containing 10 micrograms of vitamin D during autumn and winter. People who are rarely outdoors, who cover most of their skin, or who have darker skin are advised to consider it all year round. Vitamin D matters for bones, teeth and muscles; the NHS page does not present it as a mood treatment.
What does a SAD lamp do, and what does it not do?
A SAD lamp is a bright, UV-free panel used to simulate daylight in winter. The light works through the eyes, not the skin: it reaches cells in the retina that signal to the body clock, and bright light soon after waking tends to shift that clock earlier and mark the start of the day. It produces no vitamin D whatsoever, and a lamp that did would be emitting ultraviolet, which is exactly what the NHS advises you to avoid. Do SAD lamps give you vitamin D? goes through this in more detail.
What the research supports is narrower than the marketing often suggests: for people with seasonal affective disorder, bright light therapy is modestly better than placebo in pooled trials, while the NHS says the evidence is not yet strong enough to offer it routinely. Do SAD lamps work? covers the studies.
Side by side
| Vitamin D supplement | SAD lamp | |
|---|---|---|
| What it replaces | The vitamin D your skin cannot make from weak winter sun | The bright morning light your eyes do not get on dark mornings |
| Route | Swallowed; acts through blood levels | Seen; acts through the eyes and body clock |
| NHS position | Everyone should consider 10 micrograms a day in autumn and winter | Not usually available on the NHS; not enough evidence yet; choose UV-free and check with a GP |
| Time and cost | Seconds a day; a few pounds a month | 20–30 minutes a day; a one-off purchase and a small running cost |
| Does one do the other's job? | No | No |
Can you get vitamin D from a window, a walk or a lamp?
Not from a window: ordinary glass blocks most UVB. Not from a lamp, for the reasons above. A winter walk is good for many things, including daylight for the body clock, but between October and March the UK sun is too low for your skin to make much vitamin D even outdoors, which is why the NHS advice is a supplement rather than more time outside. Morning walk vs SAD lamp compares the two for the light side of the question.
Is either one a treatment for low mood?
Neither is presented that way by the NHS. Low mood in winter has many causes, and if it lasts more than a couple of weeks or interferes with daily life, the first step is your GP, who can talk through talking therapies, medication and whether a light routine is sensible for you. Winter low mood: when to see your GP explains how NHS Talking Therapies work. Keep expectations for both the supplement and the lamp in proportion.
Frequently asked questions
Should I take vitamin D if I use a SAD lamp every morning?
The lamp makes no difference to your vitamin D, so the NHS advice applies as it would to anyone else: consider 10 micrograms a day from about October to early March, and all year round if you are rarely outdoors or have darker skin.
Can I take more vitamin D to make up for the dark?
More is not better. The NHS says adults should not take more than 100 micrograms a day unless a doctor advises it, because too much over a long period can be harmful. Follow the label or your GP's advice.
Which should I buy first if I can only afford one?
A month of vitamin D costs a few pounds and is the NHS recommendation for everyone in winter, so that comes first by default. A lamp is a discretionary purchase to try if dark mornings are the specific problem; is a SAD lamp worth it in the UK? weighs it up.
Do tanning lamps or UV lamps count as light therapy?
No, and they carry real risks to skin and eyes. Light therapy for the body clock uses bright visible light with UV filtered out. The NHS advice is to choose a UV-free lamp.
Where does this leave you?
With two small winter habits that do not overlap. Take the supplement the NHS suggests, because winter sun here cannot do that job. Consider a bright morning light routine if dark mornings are what you struggle with, sit at the rated distance and give it a few weeks. And if low mood is the real problem, start with your GP. The choose your light page compares DAYARC Rise and Mini, both UV-free.
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. 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 your sensitivity to light. If you have persistent low mood or think you may have depression, speak to your GP. If you need urgent help, contact NHS 111, or call 999 in an emergency.