Quick version
Light influences your body more than you think. It affects your circadian rhythm (internal clock), your hormones, and how you feel – both physically and mentally. Daylight in the morning helps the body wake up, increases energy, and improves mood. At the same time, darkness in the evening signals the body to produce melatonin, which makes you sleepy and ready to rest.
Too little light can lead to fatigue, low mood, and poorer sleep. Too much light late in the evening – especially from screens – can instead disrupt sleep. To feel better: get daylight early in the day, spend time outdoors regularly, reduce light exposure in the evening, and maintain consistent routines.
What does light do to the body?
Light is one of the most important factors for how the body functions. When light reaches the eye, signals are sent directly to the brain, which interprets the information and adjusts the body accordingly. This means several systems are affected at the same time. Above all, light regulates your circadian rhythm, the body's internal clock, but it also affects hormone balance and how active your brain is. That is why light can make you feel more alert, more focused, and in a better mood.
Light and the circadian rhythm – the body's internal clock
The circadian rhythm is the body's way of adapting to day and night. It controls when you feel tired, when you wake up, your body temperature, and how alert you feel during the day. When light hits the eye, signals are sent to an area in the brain that acts as a “central clock”. This clock adjusts the body's functions to match the different phases of the day.
Morning light is especially important because it helps the body set the right rhythm for the rest of the day. If you get too little light – or at the wrong time – your circadian rhythm can be disrupted. This can in turn lead to sleep problems, fatigue, and reduced energy.
How light affects your hormones
Light has a direct effect on several hormones that regulate sleep, energy, and well-being.
Melatonin – the body's sleep signal
Melatonin is the hormone that makes you feel sleepy in the evening. Production increases when it gets dark and decreases when you are exposed to light. If you are exposed to a lot of light late in the evening, for example from screens, production can be suppressed, making it harder to fall asleep.
Serotonin – linked to mood and well-being
Serotonin affects your mental state and is important for the feeling of well-being. Daylight has a positive effect on serotonin, which can contribute to a better mood and more energy.
Cortisol – helps you wake up
Kortisol is a hormone that makes you alert and ready for the day. Levels are naturally higher in the morning, especially if you are exposed to light early. This is an important reason why morning light makes it easier to wake up.
Why does light make you more alert?
When you are exposed to light, the body sends signals that reduce fatigue and increase alertness. Melatonin production is suppressed, while brain activity increases. This leads to improved focus, better reaction time, and more energy. That is why even a short time outdoors in daylight can make a noticeable difference in how you feel.
What happens with lack of light?
In Sweden and other northern countries, lack of light is common, especially during autumn and winter. It can affect the body more than you might think. Common symptoms of light deficiency include:
- Fatigue and low energy
- Low mood or reduced well-being
- Poor sleep
- Difficulty waking up in the morning
These symptoms can develop gradually and are not always directly linked to lack of light, even though it is an important cause.
When light disrupts the body – negative effects
Light is not always positive. Timing plays a major role. Light late in the evening can send the wrong signals to the body and disrupt your natural rhythm. This is especially true for strong light and blue light from screens. When the body perceives this as daylight, it can prevent you from feeling sleepy at the right time. Irregular habits, such as varying sleep times or exposure to light at different times each day, can also confuse the body's internal clock. The result is often difficulty falling asleep, poorer sleep quality, and a feeling of tiredness despite having slept.
How to use light correctly in daily life
By adjusting how and when you are exposed to light, you can influence both your sleep and well-being. The most important thing is to get light early in the day. Morning daylight helps the body set its circadian rhythm and makes it easier to stay alert during the day and feel sleepy in the evening. Spending time outdoors every day, even briefly, makes a big difference. Outdoor light is significantly stronger than indoor lighting, even when it is cloudy.
In the evening, it is beneficial to dim the light. Reducing screen time and avoiding strong lighting allows the body to start producing melatonin at the right time. Sleep also improves if you sleep in a dark room. Darkness signals to the body that it is night and supports deeper, more restorative sleep.
Finally, regular routines are important. When you are exposed to light at roughly the same times each day, your body's rhythm becomes more stable.
When should you seek care?
If you have long-term problems with sleep, energy, or low mood that affect your daily life, it may be wise to seek medical care. This is especially important if the problems do not improve despite changes in habits.