Can Exposure To Light Change Our Internal Body Clock?

In this day and age, the average person gets about 6-7 hours of sleep. Our days usually start early, with lectures and office jobs starting as early as 7 or 8am. Everyone must be all too familiar with the sleepy, groggy feeling that we get in the wee hours of the morning. But is this normal? Are our late night habits correct? Or is it time for us to make some changes in our daily schedule? First, let’s see what our normal body clock tells us.

The Internal Body clock

The human body is wonderful, as it is wired in complex, yet efficient ways. However, what happens when you put diesel in a car designed to run on unleaded? Its efficiency will decrease, right? Similarly, going against our body’s normal clock decreases our own efficiency.

A biological clock is the innate mechanism in a body that regulates its various functions and behavior. It is like the body’s internal clock, which determines what functions should occur at what time. Our normal body clock is synchronized with the time of the day, i.e., night-time or day-time.

The human body has an internal clock

The human body has an internal clock

This is due to the hormone melatonin, which most of us have heard of before. Consuming coffee and caffeinated drinks “decreases melatonin levels”, but what is melatonin and what does it do?

Simply put, melatonin makes you sleepy. Of course, it has other effects too, but it’s famous for controlling your sleep patterns. Melatonin levels usually peak at night, around 2am, and then start decreasing by 7am. This is why your sleep will be deepest between 2am-4am. This is a very good argument to present to your teachers for not holding early morning lectures. Or, the next time you’re late, just blame it on your body clock! These melatonin levels are low throughout the day and start rising again around 8-9pm in the evening. This surge and drop of melatonin is due to light exposure. Our bodies are designed to function according to the availability and presence of natural light. Melatonin also affects the immune system and blood pressure. At night, with increased levels of melatonin, our elevated blood pressure levels decrease. This helps the body to relax.

Day night sun moon melatoninMelatonin level variation through the day

Circadian Rhythm

Our circadian rhythm is essentially the physiological changes that occur in our body induced by the biological clock. It is affected, primarily, by the body’s exposure to light, and follows a 24-hour cycle. Circadian rhythm is different from the body clock; they are more like a cause and effect system. The body clock is the cause – it regulates what functions need to occur and when. The circadian rhythm is the effect – a result of the regulation by the body clock. It is affected by both internal and external factors. Light is the main factor that affects it, so it is also called the light-dependent circadian rhythm. However, experiments have shown that even though we have a 24-hour cycle, people who are kept in complete darkness showed a 24.5 – 25.5 hour cycle.

The reason this is so important is that every function in our body is carried out based on a set rhythm or cycle. Therefore, any disruptions can lead to harmful effects, some small and some quite significant.

Effect of light

The commercialization of electricity has many advantages, but it has a few downsides too. One of them is artificial light. Yes, I know that artificial light is great, as I write most of these articles seated under a tube light at 12am. Even so, it screws up the normal body clock. Late-night exposure to light confuses the body into thinking that it’s still daytime, which means that less melatonin is secreted. Imagine that you don’t have a watch with you. You know that lunch will be served at 2pm, and tea will be at 5pm. You have scheduled a particular amount of work for that 3-hour time slot between 2 and 5. Now, what happens if lunch is served late, at 3pm, but tea is still at 5. Your working time gets reduced from 3 hours to 2 hours. This is basically what happens to our body. The body expects darkness at around 8pm and light again at 7. Hence, melatonin levels are scheduled to start rising at 8, but due to artificial lights, the body doesn’t get the darkness it needs until much later, but daylight is still at 7pm. Hence, the amount of melatonin your body secretes is reduced.

Artificial light in a dark room

Exposure to artificial light at night (Photo Credit : Pixabay)

This shift causes one’s melatonin levels to get messed up, which leads to a domino effect for the whole day by delaying and obstructing the normal body clock. Temperature regulation of the body, hunger, digestion, immunity, etc. are all affected by the body clock. Our immune system is the strongest at night when the body is relaxing, due to the fact that more energy can be spent on immunity, as compared to other functions. Hormones controlling metabolic activity are also regulated according to day and night. This is why a lack of sleep can hinder weight loss, as the metabolism is adversely affected. Another hormone affected by exposure to light is cortisol. This hormone wakes the body up and makes it more active. Hence, prolonged exposure to light causes an increase in cortisol levels, which contradicts the effect of melatonin. Less melatonin in the body leads to a wide range of problems, from elevated blood pressure to weakened immunity, and even sleep disorders like insomnia.

Sleep Schedule

Completely contradicting the body’s internal clock can lead to major mishaps. Now, I know it isn’t possible to change our daily routine overnight, but we can attempt to not stay up until 3am. The body can adapt to slight changes, but not to such drastic changes. Refraining from regular exposure to artificial light after 10-11pm would give the body some amount of respite. Melatonin levels drop during late morning, so scheduling important events that require an alert mind after that time slot would increase efficiency. A short relaxation period after lunch might also help, since melatonin levels increase at that point. However, if a person is caught up on sleep, that might not be necessary, as melatonin is not the only deciding factor for sleep. Planning your day around the body’s natural clock ensures maximum efficiency and output.

So, the next time your boss calls you for an 8am meeting, or your teacher schedules a 7am lecture, excuse yourself by citing “melatonin levels” and your “normal body clock”.


  1. National Institute of General Medical Sciences
  2. National Center for Biotechnology Information (NCBI) (Link 1)
  3. National Center for Biotechnology Information (NCBI) (Link 2)
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About the Author:

Mahak Jalan has a BSc degree in Zoology from Mumbai University in India. She loves animals, books and biology. She has a general assumption that everyone shares her enthusiasm about the human body! An introvert by nature, she finds solace in music and writing.

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