Can you recall a time when you are lying in bed or in a dark room starting at your mobile phone screen or your laptop? Maybe you have an email to send just before you head to bed, or you have to finish that last stage of Candy Crush before you retire to bed?

The light that is emitted from your phone or your computer is called 'blue light' and it is harmful at night. Let's see why.

Your Normal Circadian Rhythm
For millions of years, the sun has been the primary source of light for all creatures on earth, including humans.

It is rare for us to require any artificial sources of light during the day, unless we are in a closed space that lacks windows. While daytime is great for light, night is a different story. How many of you can recall a time when we did not have mobile phones, advanced electronic gadgets or energy efficient light bulbs (compact fluorescent lights, or CFL), and relied on good old tube lights or low voltage light bulbs to illuminate our houses?

Our body has an internal clock that makes it active in the day time and sleepy at night. This circadian rhythm is responsible for keeping us alert and attentive, and relies heavily on external light. The average length of one circadian rhythm is 24 and one quarter hours (24 hours and 15 minutes). This varies in people who have late nights or those who work night shifts.

Our circadian rhythm depends on the release of melatonin, a hormone released in the brain that helps us sleep. In the daytime, the hormone levels are very low, while at night they are high and help you fall asleep. However, if you are exposed to light for long hours at night by staring at your phone or computer or even when sleeping with the light on, your melatonin levels will remain low. This could alter your circadian rhythm, confusing your brain and keeping you awake for longer.

Blame The Blue
There are various wavelengths of light emitted from electronic gadgets and energy saving light bulbs. However, blue light seems to be the most notorious one. Interestingly, CFLs contain about 25% of harmful blue light and LEDs contain about 35% of harmful blue light.

In one experiment that was conducted at Harvard University, it was found that exposure to blue light for 6.5 hours suppressed melatonin release for twice as long as the same duration for green light. It also shifted the circadian rhythm by 3 hours. In another experiment conducted in Toronto, people who were exposed to bright light but were wearing blue-blocking goggles had the same levels of melatonin compared to those who were in a dimly lit room.

Another study looking at teenagers using their mobile phones or gadgets in the night found that just one hour's exposure to blue light reduced melatonin levels by 23%. In two hours, it reduced further to 38%.

Similarly, red light seems to have almost no effect on the circadian rhythm as compared to blue light. Some people even advise using a dark red light as a bed light as it would not interrupt sleep patterns.

The Harmful Effects Of Blue Light
So what effect does blue light really have on the body? Sadly, it is not just about it affecting one's sleep. Excessive exposure to blue light has now been linked to weight gain, heart disease, depression and even some forms of cancer.

Melatonin has anti-cancer properties, and low levels of it at night can increase the risk of cancer. In one study, women who worked night shifts had low melatonin levels and a 50 - 75% greater risk of developing breast cancer in their lifetime.

People who are exposed to blue light at night have a lower level of insulin production. This means that any snacks eaten when staying up late are not broken down into glucose and used by the body. Instead, they are converted to fat and increase body weight. Not just that, the low insulin levels mean that diabetes can be a complication of blue light exposure.

But it is not just adults who are affected. Children seem to be greatly impacted by blue light as well. Children and infants who stare at their favourite cartoon on your mobile phone are exposed to great amount of blue light. This can penetrate the eye, damaging the back of the eye i.e. retina. It leads to a condition called macular degeneration, which is a leading cause of blindness in adult life. It can also speed up the development of cataracts.

Preventing Damage
So what can you do to prevent the ill effects of blue light on your health? Some simple steps are sufficient. Make sure you spend plenty of time out in normal daylight. You could shift your work desk near the window. Avoid using your phone or laptop for at least 3 hours before you head to bed. This will allow your brain to increase the levels of melatonin, and this will help you fall asleep sooner.

These days, apps are available for phones that filter out the blue light and only emit less harmful rays.

Do your best to expose yourself to plenty of bright light during the day. Natural light is the best kind for you. On the weekends, try and avoid being a couch potato and head out of the house with the family.

If you have to use a bed lamp, use a red coloured one rather than a blue one. The red light has the least effect on melatonin and does not affect circadian rhythm. Avoid using LED lights too frequently.

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