As you know, light consists of a range of colours. Each colour has a different energy frequency or wavelength. The graph below shows this spectrum.
Blue light down to violet and ultra violet (UV) light has a powerful effect on the human body. From an evolutionary perspective we only experienced blue or UV light during the day (from the sun).
When there was no blue light present it meant sundown and darkness.
However today, we are flooded in blue light 24/7. We carry artificial suns in our pockets. Every time we look at our smartphone we send a signal to the brain that the sun is up.
This impacts our circadian rhythm, our sleep, and our health. You can see more about how this happens and the studies that prove this point here.
The problem with modern devices such as cell phones, LED light bulbs, TVs and other forms of energy efficient light is that these put out a lot of light in the blue spectrum.
If we limited our use of these devices to during the day it would be fine. However most of us continue to use these items well past sundown.
You can see in the image below how various light bulbs have different levels of blue light and their effect on melatonin (the sleep hormone).
So what can we do about it? The simple is to avoid artificial light past sun down. If thats not possible then you need to use the strategies discussed on the page 'How to Minimise Blue Light' or you can use the products sold here at BlockBlueLight.com.au
There are two methods:
What is the connection between light, circadian rhythm, and sleep? The answer is melatonin.
Melatonin is a hormone secreted by the pineal gland in response to darkness. It is commonly referred to as "the sleep hormone," but it also plays a vital role in controlling inflammation levels in our body while aiding our immune system (this is why, if you have a few nights of insufficient sleep, you’ll often catch a bug or become run down). It achieves this through its antioxidant properties. When people ask me what antioxidant supplements they should take I tell them to save their money and get their sleep back on track first.
Melatonin is generated after about 4 hours of darkness (the kind where you can’t see your hand in front of your face ) and generally peaks around 2am.
It runs opposite to cortisol: when melatonin is high, cortisol is low in this state, you should be sleepy. When melatonin is low, cortisol is high, you should feel alert and energized for the day. A good picture of this relationship can be seen here:
Source - http://en.licht.de
Melatonin is also the link between sleep and fat loss, as melatonin causes leptin to be released during sleep. Leptin (the hormone that causes you to feel full after a meal) enters the hypothalamus, your thyroid is up-regulated, your metabolism increases, growth hormone is released, and the body burns fat.
Circadian dysfunction is linked to obesity and it appears that leptin is the key. Researchers are finding that circadian clock deficiency or chronic jet lag leads to leptin resistance, and leptin resistance creates hormonal irregularity and fat gain. This is the body fat that, no matter how hard you train or how strict your diet, just won't go away. Hormonal cycles are crucial not only for sleep but for maintaining a healthy weight.
As we outlined above, light, and blue light in particular affects our circadian rhythm. Light influences melatonin secretion, with blue light having a far greater impact than red light.
The Harvard Health Publication sums it up nicely: "While light of any kind can suppress the secretion of melatonin, blue light does so more powerfully. Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to exposure to green light of comparable brightness. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours)" ("Blue Light Has a Dark Side").
Modern technology is the worst source of blue light in today’s environment. A study appearing in The Proceedings of the National Academy of Sciences titled, “Evening use of light-emitting eReaders Negatively Affects Sleep, Circadian Timing And Next Morning Alertness” found that "The use of light-emitting electronic devices [...] before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses [...] melatonin, reduces the amount and delays the timing of REM sleep, and reduces alertness the following morning" (8).
This study on fruit flies found that a single pulse of light to the brain was enough to disrupt circadian rhythm by 2 hours!
If you’re still not convinced that artificial light at night can impact circadian rhythm, melatonin secretion, and sleep, then here are a few more studies to prove my point:
A paper in The Journal of Clinical Endocrinology & Metabolism titled “Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans” found that, "Compared with dim light, exposure to room light before bedtime suppressed melatonin, resulting in a later melatonin onset in 99.0% of individuals and shortening melatonin duration by about 90 min. Also, exposure to room light during the usual hours of sleep suppressed melatonin by greater than 50% in most (85%) trials" (9).
In another study, dim light exposure at night was shown to disrupt circadian rhythms and lead to an increase in bodyweight (10). The study used a light source emitting 5 luxes of light. Remember, moonlight is about 1 lux. So that green charging light glowing on your bedside table could be impacting your sleep.
Finally, if you have light-coloured eyes you need to be even more careful about night time light, as it has been shown that your eye colour can affect melatonin secretion (11). Researchers found that people with light-coloured eyes are more sensitive to melatonin light suppression than those with darker eyes.
So which sources of artificial light emit blue light? Let’s look again at that chart from earlier:
We can see that modern LED and fluorescent lights contain high amounts of blue light. The researchers who created this chart also tested how each light sources affected melatonin, and found that high levels of blue light had the greatest effect on melatonin suppression. Brightness was also a determining factor.
There’s an excellent site called fluxometer that shows you the light output of various devices, ranging from the iPhone to streetlights. I recommend heading over there and playing around. It will also show how bright the light from a device is compared to daylight, and the resulting circadian rhythm phase shift. Here's a screenshot from the iPhone 6 report.
Takeaway: Light exposure at night shuts down melatonin production with blue light having a huge impact compared to red light. Blue light sources include modern light bulbs, computer screens, cell phones, and TVs.
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