Many people think that getting better sleep depends only on what they do before going to bed. They may avoid caffeine, switch off electronic devices, or try to relax before sleeping.
While these habits are helpful, new research suggests that one of the biggest influences on sleep actually happens much earlier in the day.
According to a study led by researchers at the University of Manchester, spending more time in bright daylight and keeping daily light exposure consistent may help people fall asleep earlier, sleep more deeply, and enjoy better-quality rest.
Sleep is essential for both physical and mental health. During sleep, the brain processes information, stores memories, and removes waste products that build up during the day. The body repairs muscles, strengthens the immune system, and releases important hormones.
When people regularly get too little sleep or poor-quality sleep, they may experience tiredness, poor concentration, mood changes, and a higher risk of long-term health problems such as heart disease, diabetes, obesity, and depression.
One reason sleep is so closely linked to health is because it is controlled by the body’s internal clock, known as the circadian rhythm. This natural clock tells the body when to be awake and when to prepare for sleep. The strongest signal controlling this clock is light. Bright daylight tells the brain that it is daytime, while darkness tells it that it is time to rest.
Unfortunately, modern life often disrupts this natural pattern. Many people spend most of the day inside offices, schools, or homes where lighting is much dimmer than natural sunlight. Later in the evening, they are surrounded by bright lights from televisions, computers, and smartphones that can delay sleep.
Scientists have already shown in laboratory studies that light affects the body’s internal clock. However, they wanted to know whether the same effects could be seen during normal daily life outside the laboratory. To answer this question, the research team followed 89 adults as they continued their usual routines.
Each participant wore a wearable light sensor that measured melanopic light, the type of light that has the strongest effect on the body’s biological clock. They also wore a consumer sleep tracker and completed daily sleep diaries.
Altogether, the researchers collected more than 500 days of information, giving them a detailed picture of how light exposure and sleep were connected in everyday life.
The results showed several clear patterns. People who spent more time in brighter daytime light generally fell asleep earlier and woke up earlier.
Participants whose daily light exposure remained steady from one day to the next also had healthier sleep schedules. In addition, people who avoided large swings between very dim and very bright light experienced more deep sleep during the first half of the night.
Deep sleep is especially important because it is the stage when the body carries out much of its repair work. It supports learning and memory, strengthens the immune system, and helps people wake up feeling refreshed. The researchers found that stable light exposure appeared to strengthen this important stage of sleep.
The team also compared the information from wearable devices with what participants reported in their sleep diaries. Most of the time, people judged their sleep fairly accurately. However, when deep sleep or REM sleep was reduced, their own opinions became less reliable than the measurements recorded by the devices.
The researchers believe these findings carry an important public health message. Spending more time outdoors during the day, sitting near windows when possible, and maintaining regular daily routines may help support healthier sleep without medication.
At the same time, reducing unnecessary bright light at night may help the body’s natural clock function more effectively.
The study was led by researchers at the University of Manchester and published in the journal npj Biological Timing and Sleep. Although the research does not prove that brighter daylight alone causes better sleep, it provides strong real-world evidence that healthy light habits are closely linked to healthier sleep patterns.
Larger studies will help confirm the findings, but the results suggest that one of the simplest ways to improve sleep may be to spend more time enjoying natural daylight every day.
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