Light and the Sleep Connection

Light is what governs when we are awake and when we are asleep, particularly sun light.

On the face of it, it is quite simple but people tend to make a big mess of it.

Let’s break it down what is going on in our brain and body when we go through one 24 hour day.

Let’s start with waking. regardless of how well you slept or how poorly you slept, most of us tend to wake up sometime around when the sun rises, or within a few hours of the sun rising.

If we have been asleep adenosine levels tend to be low and our system generates an internal signal that is in the form of a hormone, this hormone is cortisol.


Cortisol is released from the adrenal glands, the adrenal glands sit above the kidneys. Also adrenaline along cortisol is released and this makes us feel awake.

Now the release of cortisol and adrenaline might be coming from the alarm clock, or from us naturally waking up and it alerts the whole system that it is time to increase heart rate, time to start tensing muscles and is time to start moving about.

It is HUGELY important that this cortisol release comes early in the day. It is very normal and healthy to have this increase of cortisol early on in the day.

When this happens a timer is set off in your system that dictates when melatonin (The sleep hormone) will be secreted from the brain later on in the day.

When you wake up there is a timer that starts going that tells your brain and body that in about 12 to 14 hours a different hormone (melatonin) will be released from your pineal gland.

So Cortisol is the signal of waking and melatonin is the sleepiness signal, the trigger of the waking signal triggers the timer of the sleep signal.

Why is light important?

When we wake up and open our eyes, we get light, when light goes into the eye there is an electrical signal in the brain to the internal clock that resided above the roof of our mouth called the suprachiasmatic nucleus which has connections with every cell and organ in our body.

It is vitally important that we get light communicated to the internal clock in order to time the cortisol and melatonin properly. If we don’t get this right there are huge, broad problems on cardiovascular, dementia, metabolic effects, learning, depression, in fact there are so many negative effects associated with getting this wrong its key we do this correctly.

When we wake up our eyes open, if we are in a dark room there is enough light to to trigger the correct timing of this cortisol, melatonin connection. The neurons in our brain respond best to sunlight, this happens particularly when the sun is low in the sky, this is because there is a particular contrast between