Blue light and Homeostasis
Visible light is made of 'waves' of varying lengths that correspond to different colours. These lightwaves, in particular short waves of blue light, are responsible for synchronising our internal clock, also known as the circadian rhythm, to the external day/night cycle.[1] This synchronisation occurs in the suprachiasmatic nucleus situated in the hypothalamus, a brain region associated with maintaining homeostasis in our bodies.[1] Homeostasis refers to the balance required among systems in our bodies that allows them to optimally function, which suggests sleep is very important for our bodies to function!
How do we feel sleepy?
The pineal gland in the brain is responsible for producing and secreting a hormone called melatonin that is responsible for making us feel sleepy.[1] In response to blue light signals from the retina in the eyes during the day, the suprachiasmatic nucleus instructs the pineal gland to suppress its production of melatonin.[1] Without blue light stimulation, the suprachiasmatic nucleus stops suppressing the pineal gland and the resultant increase in melatonin secretion causes us to feel sleepy and want to go to bed! This would naturally occur at night as it becomes dark outside; however, as the screens we use in all parts of our daily life also emit blue light, this can disrupt this natural cycle in the body, by suppressing melatonin when it's dark.[1] This means that the activity you're trying to use to relax and go to sleep, is actually working against you!