How light affects sleep

How light affects sleep

If you’ve ever wondered how light affects sleep, this is for you. Sleep is essential to health. If you are sleep deprived – either in terms of quantity or quality – this is bad. Most of us can survive a bad night’s sleep. But several bad nights in a row. Or weeks, or months of poor sleep has been linked with all sorts of bad health outcomes.

Warning: If you are already sleep deprived, please don’t allow this article to stress you. Sleep anxiety is a real thing too. It would be ironic if reading this caused you more sleep problems. Use it to inform and empower you.

Does light affect sleep?

Yes, definitely. In fact light is perhaps the most powerful effectors of sleep. Especially daylight. You see we all have a clock inside us. It’s called the “circadian clock”. And it is set by exposure to light. To be precise, particular bandwidths of light. And all of those are found in daylight.

Daylight and sleep

You are likely to wake up around sunrise. Of course this will vary throughout the year – particularly if you are further from the equator. Or a shift-worker.

What stimulates waking is an increase in cortisol release. You may think about cortisol as a “stress hormone”. But we all have cortisol rising and falling in us all of the time. And you need this rise first thing in your day to help you get going.

When you get up also sets the clock on when your melatonin will start to be released – about 12 to 14 hours later. So waking up and getting going sets the timer for when melatonin will be released. Melatonin is often referred to as the “sleep hormone”.

There is a cycle of rising cortisol early in the day and then dropping away; and rising melatonin in the evening and slowly dropping through the night. This surge of cortisol is best stimulated by the eye being exposed to early morning light. There are qualities of early morning light that stimulate this surge better than light at any other time of day. And better than any type of artificial light.

It’s all to do with a particular type of cell in the eyes – Retinal Ganglion Cells. Viewing light through a window is 50 times less effective than being outdoors in the natural daylight.

Having this early surge in cortisol – far away from your melatonin surge – is really important to your health and sleep cycle.

What if there isn’t enough light?

What should you do if you live somewhere where days are short and the light is dim? Get out doors for longer as soon as the light is up. You can supplement with artificial light that simulates daylight or light that contains a lot of “blue light”.

Be careful NOT to look at light directly – it can damage the eyes.

Yes, you should avoid blue light late in the day. But it’s blue light that will help in the morning.

Avoid bright light in the evenings

Bright light suppresses melatonin. You don’t want to do that late in the day. So, in the evenings, turn the lights down. If you have to use a computer or smartphone, then use blue-light blockers. If you need lights on, try to make them uplighters rather than bright ceiling lights.

What about sunglasses?

If you have to block out bright light, so be it. It’s important to protect your eyes. However, if at all possible, make sure you get that early exposure to daylight. So, unless you really need them, don’t use sunglasses early in the day.

What if you’re blind? It still works. You don’t have to see the sunlight. These Retinal Ganglion Cells will still detect the light.

Summary of light and sleep

Get early exposure to daylight – or bright light that simulates daylight (as soon after you get up as possible)

Avoid bright lights in the evenings – use blue blockers if you need to use screens, and turn the lights down

In case this article on how light affects sleep hasn’t helped enough…. If you’re still struggling with sleep, connect with one of our sleep coaches here on Active X Health.


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