Like so much in our day-to-day lives, it can be easy to take something as common as light for granted. But, light does a lot more for us than help us see and make the world a brighter place. Many of our physiological processes are actually controlled by light.
Via our nerve fibers, receptors in the retina transmit light information directly to the brain where these stimuli trigger various responses from our hormonal and nervous systems. This interconnection is the reason why aspects of our wellbeing such as stress, immunity and regeneration are influenced by light.
Light also acts as the conductor of our circadian rhythms, which are all the changes that happen in our bodies throughout the course of 24-hour periods. And, because our internal master clocks control the production of melatonin, our circadian rhythm influences our sleep-wake cycles.
Melatonin is the hormone that makes us drowsy. When our optic system transmits the signal that less light is present—or that it is dark—then our brains respond by emitting more melatonin. The hormone has a calming effect and slows down certain bodily processes. Thus, melatonin levels in the human body tend to be highest between 2 and 3 am.
Conversely, the release of melatonin is reduced during times that our bodies receive more light. When we are in a bright environment, the concentration of the "happiness" neurotransmitter serotonin rises. Where melatonin inhibits, serotonin stimulates: circulation, body temperature and sex drive are being activated.
Knowing these relationships and the interaction of melatonin and serotonin can help you better understand the importance of darkness for deep, restful sleep. For example, research by biologists at the Johns Hopkins University found that light at night can cause depression in mice. It is assumed that it affects humans similarly.
Every light source inhibits melatonin release and prevents deep sleep. Blue light, as emitted by smartphones or tablets, can be especially harmful—these particular light waves are leading culprits in today's growing issue of sleep deprivation.
And other nocturnal light sources can adversely affect our ability to sleep as well. A street lamp in front of the window or light coming into the bedroom from the hallway can have negative effects.
So, if you are having trouble sleeping, double-check for light that may be interfering with your body's ability to slow down and relax at night. Keep your sleep sanctuary as dark as possible so you can enjoy the benefits of rejuvenating rest and wake up inspired!