How light exposure impacts your sleep and what you can do about it.


Scientific Education

“Sleep is the single most effective thing we can do to reset our brain and body health each day.”
Matthew Walker, Why We Sleep, 2017

In our modern world, sleep is invaluable for maintaining physical health and cognitive function. Poor sleep quality is linked to an increased risk of mood disorders, anxiety, and cognitive decline, as well as reduced immune tolerance, poor appetite control and increased inflammation. While it can be strongly impacted by our stress levels, diet, and exercise among other factors, perhaps the biggest influence determining sleep quality is our exposure to light. Many people take light exposure for granted; we flick switches to illuminate our homes, spend hours engrossed in the glow of screens, and sometimes forget to access daylight without thinking about the impact that it has on our health. However, the quality and timing of our light exposure significantly impact our hormonal balance and sleep patterns from the minute that we wake up in the morning. We’ve summarised the ways in which environmental light exposure influences sleep and offered practical suggestions to help you achieve a better night’s rest.

The circadian rhythm is the body’s internal clock – regulating various physiological and behavioural processes over a 24-hour cycle. It has evolved to enable humans to optimise energy expenditure and the internal physiology in direct relation to the natural world. Exposure to sunlight is the most potent cue for entraining our circadian rhythms – helping to synchronise our internal clock with the external world.

Multiple studies have shown that outdoor exposure to sunlight early in the day (as opposed to light through a window) can best improve sleep quality, mood, and alertness during the day. This is because viewing full-spectrum daylight stimulates a rise cortisol in the morning. This hormone makes the body feel alert and stimulates metabolic processes during the day, while also setting a biological timer for sleep onset that evening. The research on exactly how much morning sunlight exposure we need is limited as the environment and individual core body temperature are influential factors, but recent studies have recommended to aim for at least 5 minutes (in direct sun), ideally 30 minutes. Time outdoors throughout the day further improves sleep quality. Then as the day progresses into the afternoon, the sun emits fewer blue light waves while red light increases close to sunset, enabling the body to discern that night is drawing in. Cortisol levels decline, and melatonin increases, triggering the feeling of sleepiness.

Within the context of the built environment, this understanding of how light controls our circadian rhythm is crucial. While artificial light has brought immense convenience and productivity gains, it can also be a double-edged sword when it comes to sleep. In particular, bright blue light emitted by screens, such as smartphones, tablets, and computers stimulates cortisol production in the body. This might be useful during working hours, but nighttime exposure results in elevated cortisol and supressed melatonin levels which tricks the body into thinking it’s still daytime and impacts sleep. Evidence shows that even a single bedside lamp or a low-lit room that emits the equivalent of 1-2% daylight (200lux) can delay melatonin release by 90 mins. Symptoms of insomnia are also associated with areas of high light pollution overnight, so sleeping in total darkness is key.

Understanding the impact of environmental light exposure on sleep provides a foundation for adopting interventions to enhance sleep quality. Here are some evidence-based strategies:

1. Maximize natural light exposure during the day:

  • City Sanctuary developments includes east facing bedroom windows where possible to maximise early morning natural light levels in bedrooms.
  • Take breaks and go for walks outside during the day.
  • Research has shown that for every hour spent outdoors during the day, the odds of chronic insomnia could decrease by up to 18%.
  • Aim to see the sunset to reduce cortisol levels and prime the system for rest.

2. Reduce artificial light exposure in the evening:

  • Limit screen time, especially from smartphones, tablets, and computers, at least one hour before bedtime.Use “night mode” or blue light filters on electronic devices to reduce the impact of artificial light on melatonin production.
  • Use red-lensed blue-light blocking glasses that have been shown to improve melatonin levels by reducing exposure to blue light from devices.
  • Limit overhead lights in the evening, opting for desk and table lights which have a lower visual field. City Sanctuary uses 5a circuits in bedrooms to allow easy use of bedside table lights from the main light switch.

3. Use better quality lighting:

  • City Sanctuary developments use warm, dimmable lighting for use during the evening to reduce cortisol production.We are also rolling out the use of smart lighting systems that can be programmed to mimic the natural progression of daylight.

4. Create a sleep-enhancing bedroom:

  • Make your bedroom as dark as possible by using blackout shades – this is something that we provide in our City Sanctuary developments.Keep electronic devices out of the bedroom to minimise exposure to artificial light at night.

5. Establish a consistent sleep schedule:

  • Go to bed and wake up at the same time every day, even on weekends. This consistency helps regulate your circadian rhythm and optimise your sleep patterns.

6. Consider light therapy:

  • Light therapy boxes or SAD lamps (min 10,000 lux) that mimic natural sunlight can be useful for individuals who have minimal access to natural light during the day. Typically priced between £40 and £200, these can be useful for helping to increase alertness in the mornings (particularly in the winter months), supporting focus when working from home throughout the day, and for shift workers. More guidance can be found here.

Our exposure to environmental light, whether from the sun or artificial sources, significantly impacts our sleep quality. By adopting evidence-based interventions, such as maximising natural light exposure during the day and minimising artificial light use at night, you can take proactive steps to promote a more restful night’s sleep. At City Sanctuary, we’re continuously staying abreast of the research that identifies the extent to which we can improve our developments to optimise health, and applying this learning where we can.

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