Seasonal affective disorder (SAD) is a type of depression that follows the seasons: for most people it starts in autumn or winter and lifts in spring or summer. The NHS describes the main symptom as depression that happens in the winter and goes away in the summer. SAD can affect your mood, sleep, appetite and energy for months at a time, but it is a recognised condition and it is treatable.
We should be upfront: Nordic Light Lab sells light therapy lamps, which is exactly why we want to be honest about what light can and cannot do. For many people a SAD lamp can relieve the symptoms of SAD, but it does not cure depression and it is not a replacement for medical care.
Seasonal affective disorder symptoms
The symptoms of SAD are the symptoms of depression, but they follow a seasonal pattern that tends to repeat year after year. According to the NHS, they can include:
- a persistent low mood
- losing interest in things you normally enjoy
- feeling guilty, hopeless or worthless
- feeling restless or irritable
- difficulty concentrating
- feeling hungrier than usual and eating more
- feeling more tired than usual and sleeping more
- thoughts of suicide or self-harm
The pattern is the important clue. If the same symptoms arrive as the evenings draw in and fade as the days lengthen, mention that to your GP.
If you need help right now: if you are having thoughts of suicide, or you do not feel you can keep yourself safe, call 999 or go to A&E. You can also call Samaritans free, any time of day or night, on 116 123. For urgent mental health advice that is not an emergency, call NHS 111. More options are listed on the NHS page where to get urgent help for mental health and on the Samaritans website.
When does seasonal affective disorder start, and what causes it?
For most people with SAD, symptoms begin in autumn as the days shorten and ease in spring. Less commonly, some people have a summer pattern. Around the winter solstice there are fewer than eight hours of daylight in London and roughly seven in Edinburgh, and most of us spend those hours indoors, where ordinary lighting is typically a few hundred lux. Outdoor daylight, even on a cloudy day, is usually many times brighter.
The NHS says the exact cause of SAD is not fully understood, but the main theory is that a lack of sunlight affects how the brain regulates mood and sleep. Three mechanisms are usually discussed:
- Your circadian rhythm. Your body clock uses light, especially morning light, to keep time. Dark mornings can let it drift, leaving you groggy.
- Melatonin. Darkness prompts the release of melatonin, the hormone that makes you sleepy. With less light, people with SAD may produce more of it, which could explain the extra sleepiness.
- Serotonin. Less sunlight may be linked to lower serotonin activity. Serotonin is a brain chemical involved in mood, appetite and sleep.
These are theories rather than settled facts, and SAD is likely to involve more than one factor.
SAD vs the "winter blues"
Plenty of people feel slower in winter: wanting more sleep, craving comfort food, struggling on dark mornings. That is often called the winter blues, and it does not stop you living your life. SAD is different in two ways: the symptoms are strong enough to get in the way of work, relationships or looking after yourself, and they come back season after season. A useful rule of thumb: if low mood has lasted a couple of weeks or more and is affecting everyday life, speak to your GP rather than waiting for spring.
Seasonal affective disorder treatment: what the NHS recommends
The NHS lists several approaches to treating SAD, and many people combine more than one:
- Lifestyle measures: daylight, exercise and routine (see below).
- Talking therapy, such as cognitive behavioural therapy (CBT). In England you can refer yourself to NHS talking therapies.
- Antidepressants, which your GP may suggest, particularly for more severe symptoms.
- Light therapy: a bright light, often called a SAD lamp or light box, that simulates daylight.
The NHS says light therapy is not usually available on the NHS because there is not enough evidence to tell whether it is effective, although many people find it helpful. The research that exists is encouraging. A 2005 meta-analysis by Golden and colleagues in the American Journal of Psychiatry pooled eight studies of bright light therapy for SAD and found a significant reduction in depression symptoms, with an effect size of 0.84. Dawn simulation, pooled from five studies, showed an effect size of 0.73. Those are fairly large effects, but from a small number of studies. A 1998 trial by Terman and colleagues in the Archives of General Psychiatry, involving 158 people with winter depression, found morning light produced more remissions than evening light, which is why morning use is the standard advice.
How to use a SAD lamp properly
- Brightness: 10,000 lux. The NHS says 10,000 lux is standard and that a lamp should be UV-free and carry a UKCA or CE mark. Brightness drops quickly as you move away, so the lux figure only applies at the distance the manufacturer specifies.
- Time: typically 20–30 minutes. This is the usual guidance at 10,000 lux. Some manufacturers suggest longer sessions, so follow the instructions for your lamp.
- Timing: in the morning. Use it soon after you get up, for example over breakfast. Avoid late evenings, as it may make it harder to fall asleep.
- Position: to the side, not in your eyes. The light needs to reach your eyes, but do not stare into it. Carry on reading, eating or working.
- Consistency: every day. Use it daily through the darker months and give it a couple of weeks before judging whether it helps.
Check with your GP before starting if you have bipolar disorder, an eye condition, or take medication that makes you more sensitive to light. For a detailed comparison of what to look for, see our SAD lamp UK buying guide.
Self-help for SAD: daylight, movement and routine
Light therapy works best alongside the basics, most of which cost nothing:
- Get outside in daylight, ideally in the morning. An overcast walk still gives you far more light than a well-lit office. Indoors, sit near a window.
- Move every day. Exercising outdoors gives you light at the same time.
- Keep a steady sleep routine. Wake at the same time every day, including weekends. A sunrise alarm clock can make dark mornings gentler, but it is not a substitute for a 10,000 lux lamp.
- Stay connected with friends and family, even when you would rather hibernate.
- Go easy on alcohol and screens before bed, both of which can disturb sleep.
A note on vitamin D. The NHS advises everyone in the UK to consider a daily 10 microgram vitamin D supplement during autumn and winter, for healthy bones and muscles. It does not recommend vitamin D as a treatment for SAD, and the evidence that it improves SAD symptoms is unclear.
When to see your GP
See a GP if you think you might have seasonal affective disorder, if low mood is affecting your daily life, or if you have already tried treatment and it is not working. Your GP may ask about your mood, sleep, eating habits and whether your symptoms change with the seasons. If you are having thoughts of suicide or self-harm, do not wait for an appointment: call 999, NHS 111 or Samaritans on 116 123.
Our light therapy lamps
If you would like to try light therapy at home, we stock three lamps from Innolux. According to their product pages, all three deliver up to 10,000 lux.
- Innolux Epic: a slim, round lamp 23.5 cm across, giving 10,000 lux at about 20–30 cm from your face, with three colour temperature settings.
- Innolux Lempi: an acrylic and ash design with adjustable brightness and colour temperature, also used at about 20–30 cm.
- Innolux Valovoima Desk: a full-size desk lamp designed by Harri Koskinen, with stepless dimming, so it doubles as an everyday work light.
Compare them side by side on our light therapy lamps page. Whichever you choose, a lamp supports you through winter; it does not replace your GP.
Frequently asked questions
What is seasonal affective disorder?
Seasonal affective disorder (SAD) is a type of depression that follows a seasonal pattern. For most people it starts in autumn or winter and improves in spring or summer. Symptoms include low mood, loss of interest, tiredness, sleeping more and eating more.
When does seasonal affective disorder start?
For most people, SAD symptoms start in autumn as the days get shorter and tend to feel worst in the darkest months of winter. They usually ease in spring. A smaller number of people have a summer pattern instead.
What causes seasonal affective disorder?
The exact cause is not fully understood. The main theory is that reduced daylight in winter disrupts the body clock and affects melatonin, which controls sleepiness, and serotonin, which is involved in mood, appetite and sleep.
Do SAD lamps actually work?
Many people find them helpful. A 2005 meta-analysis in the American Journal of Psychiatry found bright light therapy significantly reduced SAD symptoms, but it pooled only eight studies. The NHS says there is not yet enough evidence to offer it routinely. A SAD lamp can relieve symptoms; it does not cure depression.
How long should I sit in front of a SAD lamp?
Typically 20–30 minutes a day at 10,000 lux, in the morning, at the distance the manufacturer specifies. Some manufacturers recommend longer sessions, so follow the instructions for your lamp.
Can I get a SAD lamp on the NHS?
Usually not. The NHS says light therapy is not usually available on the NHS because there is not enough evidence to tell whether it is effective. If you buy one, the NHS advises choosing a lamp that is 10,000 lux, UV-free and has a UKCA or CE mark.
Is a sunrise alarm clock the same as a SAD lamp?
No. A sunrise alarm clock gradually brightens before your alarm to make waking up gentler. A SAD lamp gives a much brighter light, typically 10,000 lux, that you sit in front of for a set time. Some people use both.
Does vitamin D help with seasonal affective disorder?
The evidence is unclear. The NHS advises everyone in the UK to consider 10 micrograms of vitamin D a day in autumn and winter for bone and muscle health, but it does not recommend vitamin D as a treatment for SAD.