Sunlight is white light with all visible colours of the rainbow, VIBGYOR, from violet to red. Violet is the shortest wavelength (380 nanometers) and red is the longest wavelength (740 nanometers) that we can see. Within this visible range, blue light occupies about 450 to 495 nanometer wavelength.
When we see the sun at sunset, we see it through thick layer of atmosphere towards the horizon. The shorter wavelengths like green blue violet are scattered by this thick atmosphere, so only the longer wavelengths red, orange, yellow reach us, giving sunsets their typical yellow orange red colour. During daytime blue light is scattered by air molecules but still reaches us as the layer of atmosphere through which it must pass is much narrower. Hence the sky looks blue during day time. See the short explanation on Stanford university website. http://solar-center.stanford.edu/SID/activities/GreenSun.html
Our human body has evolved with nature. In the presence of bright light during the day, particularly blue light, it produces hormones like cortisol that make us alert and active. As skies get redder and darker towards the evening and night, our body produces melatonin hormone which makes us relaxed and sleepy. This cycle of human awake and asleep state controlled by light is called circadian cycle, or sleep cycle. Apart from sleep it also affects other metabolism, hunger & food habits, body temperature, heart rate, hormone production, repair and regeneration of body cells, alertness and brain activity.
The circadian rythm or sleep cycle is affected by all artificial light including LEDs, fluorescent bulbs and incandescent bulbs. Artificial light confuses the body that night is day and melatonin production is suppressed. But blue light produces the highest amount of such detrimental effect. Red light has the least effect. White LEDs are particularly problematic because they contain a high amount of blue.
What is the mechanism by which light and particularly blue light affects the circadian rythm? We know that light sensitive rod and cone cells are present in the retina which enable us to see things. There are a third type of light senstive cells called intrinsically photosensitive retinal ganglion cells (ipRGCs) which do not produce vision but enable various light sensitive reflexive responses in the brain and body. Their sensitivity to light and dark is thanks to a protein called melanopsin. They are connected to various parts of the brain including the supraschiasmatic nucleus (SCN) of the hypothalamus. SCN is considered brain's master clock. When ipRGCs send signals to the SCN regarding light and dark, the SCN trains the circadian rythm by associating this with sunrise and sunset. SCN regulates the circadian rythm through pineal hormone melatonin. circadian cycle is most affected by blue light because melanopsin reception in ipRGCs is particularly sensitive to blue light between wavelengths 459 and 485 nanometers wavelength with peak sensitivity at around 480 nanometers, all wavelengths of blue light.
Before we come to blue light let us see what kind of observations have been made regarding light, sleep & health. According to Harvard Health Letter night time light exposure throws body's biological clock, the circadian rythm out of whack, sleep suffers and it may contribute to causation of cancer, diabetes, heart disease, obesity, depression. https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
Exposure to light and particularly blue light suppresses secretion of melatonin. Preliminary experimental evidence shows lower melatonin's association with cancer.
In another study, at Harvard, researchers put 10 people on a schedule that gradually shifted the timing of their circadian rythms (by suitable night time exposure to light). Their blood sugar level increased, throwing them into a prediabetic state. Levels of leptin, the hormone that leaves people feeling full after a meal went down. So night time exposure to light may cause diabetes and obesity.
Night light is the reason many people do not get enough sleep and researchers have linked short sleep to increased risk for depression as well as diabetes and cardiovascular problems.
As we have said earlier, melanopsin reception in the ipRGC cells of the retina is particularly sensitive to blue light between wavelengths 459 & 485 nanometers. The peak sensitivity at around 480 nanometers. This was determined by testing 72 people in more than 700 experiments at Thomas Jefferson University to determine the strongest wavelength for Melatonin suppression. 10 published studies on humans, rodents and monkeys have also confirmed this.
So whatever harm night light generally does, blue light at night does it worse. This has also been observed in experiments.
Harvard researchers compared the effects of 6.5 hour exposure to blue light and to green light of comparable brightness. Blue light suppressed melatonin for about three hours and shifted circadian rythms by three hours while green light did so only by 1.5 hours. So blue light had about twice the effect.
In another blue light experiment, researchers at University of Toronto compared melatonin levels of people exposed to bright indoor light wearing blue-light-blocking goggles to people exposed to to regular dim light without goggles. The levels of the hormone were nearly the same, thus supporting the hypothesis that blue light is a potent suppressor of melatonin.
Blue light also proved more powerful in elevating body temperature and heart rate and reducing sleepiness and improving performance both during night and day. This is good during daytime but bad at night when you should get sleep for good health.
Speaking of all the bad sleep and health effects of blue light, we have seen in the last article that white LEDs produce way more blue light than fluorescent lamps and fluorescent lamps produce much more blue light than incandescent lamps. Their energy consumption is reverse. LED consumes least power, fluorescent lamp consumes most power and incandescent bulb consumes the most power to produce the same amount of light.
The below image repeated from the last article shows power spectrum of light for these three kind of bulbs.
[image taken from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734149/]
So what does all this mean? It means that in our quest for using LED light sources to save on electricity bills and to save the environment, we are putting our sleep and health in trouble. The Ujala scheme LED bulbs distributed by the Indian government for energy saving are likely giving us sleep problems and may lead to cancer, diabetes, heart disease, obesity, depression, etc. It means the street LEDs that municipalities around the country are putting up can make localities sleepless and potentially very unhealthy.
This isn't just a problem with India. While other countries may not have distributed LEDs like Ujala scheme, many first world countries are banning the good old incandescent lamp for its higher energy usage. Municipalities around the world are putting up street LEDs.
There is an acute need for public awareness regarding the info presented in this article so that people make a choice in their personal light usage at home and office and also oppose the use of high blue light content street LEDs being installed by municipality.
However that is not all. The blue light in the LED causes blindness too. In addition, the street LEDs that are being installed by municipalities/local councils have scanning and attack antennas inside them which serve as directed energy weapons to attack people on street and in their homes with microwaves which affect mind as well as body. We will see all this in subsequent articles on LEDs.
The information in this article is compiled from below sources:
Blue light has a dark side https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
What's in a colour? The unique human health effects of blue light. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2831986/
Effects of blue light on the circadian system and eye physiology https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734149/
Wikipedia entry for the protein melanopsin https://en.wikipedia.org/wiki/Melanopsin