Effects of blue light technology
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Blue light is a range of the visible light spectrum, defined as having a wavelength between 400−495 nm. This short wavelength means that blue light is a type of high-energy visible light, defined as having a wavelength between 400 and 450 nm. Violet, indigo, and some blue-green light are other types of high-energy visible light.
Blue light sources are becoming increasingly common in today’s environment. Exposure to blue light comes from a variety of technologies including computers, smartphones, televisions, and lights. Much of the exposure arises from light emitting diodes (LEDs). Today, many white LEDs are produced by pairing a blue LED with a lower-energy phosphor, thereby creating solid-state light (SSL). This is often considered “the next generation of illumination” as SSL technology dramatically reduces energy resource requirements.
Increasingly, people are exposed to blue light via everyday technology. The 2015 Pew Research Center study found that 68% of U.S. adults own a smartphone and 45% own a tablet computer. The study also found that levels of technology ownership vary by age; 86% of Americans 18-29 and 83% of those 30-49 own smartphone. Younger Americans also use high rates of blue light technologies. The survey of Common Sense Media in 2013 also demonstrated that 72% of children age 0–8 years old used mobile devices for watching videos, using applications or playing games. Moreover, 93% of teens owned a computer or had access to one at home. In contrast, smartphone ownership and computer rates are lower for older Americans.
Blue light exposure has been shown to impact health. Natural exposure to blue light during the daylight hours boosts people's energy, alertness and mood. However, elongated exposure to the waves transmitted through screen devices during the evening can disrupt circadian rhythm and cause various health effects including a disruption in normal sleep schedules. Scientists believe this is caused by blue-light-sensitive intrinsically photosensitive retinal ganglion cells suppressing the production of melatonin and/or stimulating the suprachiasmatic nucleus of the hypothalamus.
Effects of blue light on eye health
Blue light falls within the spectrum of high energy visible light due to its shorter wavelength. This is a result of the inversely proportional relationship between wavelength and frequency, and subsequently that frequency is directly proportional to energy. (See Photon energy) Consequently, light with longer wavelengths, such as red light, will contain lower amounts of energy and light with shorter wavelengths, such as blue light, produces greater energy. Therefore, light with shorter wavelengths have the ability to elicit physiological changes in organisms exposed to them due to the associated energy 
In some animal studies, blue light from LED sources has been shown to induce damage to photoreceptor cells. Acute exposure to high intensity light has been shown to cause photoreceptor loss in rhesus macaques and other species. Concerningly, irreversible functional loss in the rat retina due to LED exposure has been shown to occur even at domestic lighting levels. It is possible that chronic daily exposure to blue LEDs could pose similar ocular risks to humans[according to whom?]. Additionally, the severity of retinal damage has also been shown to vary by time of day[by whom?]. Rodent susceptibility to light-induced retinal damage has been shown to be three to four times higher at night than during the day. This leads to significant concern about the potential negative effect of blue light on human retinas at night. Point, however, considers that experiments on rodents do not provide evidences that light from LEDs at domestic level is deleterious for human retina,. Nevertheless, according to the same author, some concerns exist regarding the use of blue LEDs in pseudotherapies like chromotherapy  or when using LEDs in luminous toys, because eyes of young children collect more light .
Some studies also suggest that chronic blue light exposure may represent a risk for the development of age-related macular degeneration and other pathologies. Animal studies have shown that age-related macular degeneration can be induced by blue-light exposure. One epidemiological study has also shown a positive correlation between sunlight exposure - a natural source of blue light- and increased risk of early age-related macular changes in humans. However, this particular association of effects from blue light is difficult to assess in humans and warrants further study. Unfortunately, there are no studies that measure the effect of chronic blue LED exposure on age-related macular degeneration in humans as this is relatively new technology.
Furthermore, studies have shown that light with wavelengths between 400 and 450 nm can induce mitochondrial dysfunction (See Mitochondrion). With large amounts of mitochondria concentrated in the retinal ganglion cells, this presents a potential vulnerability. It is hypothesized that the mitochondrial absorbance of short wavelength, high-energy, light-including blue light could exacerbate retinal ganglion cell death. Although healthy in situ mitochondria have been shown to absorb short wavelength light without difficulty, it appears as though increased exposure to high energy light could increase retinal cell death if glaucoma, other pathologies, or aged cells are present. This could lead to increased problems due to blue light exposure by the aging population, or those in poor eye health.
Effects of blue light on sleep and circadian rhythm
Blue light vs other forms of light on sleep
An experiment in this article[clarification needed] was performed to test this idea using three variables, blue light, yellow light, and darkness. Each group was exposed to light or in the case of the control group, darkness, for before bed. The results concluded that blue light inhibited signs of sleepiness while the control group showed expected signs of tiredness and the yellow light showed no significant effect on sleep. Overall, absorbing light during the day, as opposed to night, may make a difference in falling and staying asleep.
Public health concerns regarding prolonged exposure to blue light
On eye health
Light is transmitted to the retina through the lens. In humans, the amount of light transmitted by the lens is age-dependent. In young children, more than 65% of blue light is transmitted. This transmission rate decreases over time; at age 25, only 20% of blue light is transmitted to the retina. The decreased transmission of blue light occurs as our eye’s lens naturally yellows and absorbs more blue light over time, thus preventing blue light from reaching the retina. As a result of this natural process, younger people are more susceptible to the effects of blue light.
One public health concern regarding exposure to blue light is based on the fact that children may be more susceptible to its effects. The concern is that not only are children the most vulnerable to the effects of blue light exposure but they are also more likely to frequently use devices that emit blue light and will likely be exposed to more blue light sources over the course of their lifetime. Point discusses the validity of blue light exposure values for newborn infants and concludes that "because of focal length and pupil diameter differences, limit for effective blue radiance for newborn infants could be around 2.8 times lower than for adult", what calls for particular caution with luminous toys. However, this author suggests the fact that higher transparency of crystalline lens of newborn infants could increase risk from technologies as halogen lamps and fluorescent lamps, which are rich in violet light, but not the risk from LEDs, which are free from violet light.
Although older adults absorb less blue light, possible eye damage from prolonged exposure may occur. The relative newness of blue light technology and its ubiquitous use in society creates questions for which there are no known answers yet. Continued research into the cause and effect of the dose-relationship of exposure to blue light and negative health effects should be studied and reasonable policy recommendations (such as limited screen time for young children) should be considered as prudent measures until more information is available.
On circadian rhythm and sleep
The average sleep time has significantly decreased over the last two decades. Teens typically need to receive nine hours of sleep a night. But, statistics reveal that less than twenty percent actually do receive enough sleep each night. People who do not get enough sleep each night, tend to eat more because a hormone stimulates their appetite, exercise less, and become more depressed. Looking at a screen before bed increases your alertness and may prevent you from falling asleep right away. A study has discovered teenagers are more likely to exhibit behavior problems and have trouble paying attention during the day if they spend time on blue light devices at night.
Lack of sleep has consequences for teenagers. A study found that over seventy percent of teenagers get less than eight hours of sleep each night, and less the ten percent receive the recommended nine hours of sleep. Not getting enough sleep can make you more prone to diseases or obesity. Just one night of irregular sleep can drastically cause an imbalance in our bodies. Because blue light is the color of the sky, this may be the reason it is extremely sensitive to our eyes. Blue light has been found to delay sleepiness and can affect our circadian rhythm. Wearing yellow tinted sunglasses at night to avoid the blue wavelengths can ensure that you will become naturally tired and may help induce sleep quicker.
A research study measured the effect of iPads at full brightness. It was found that after one hour of use, there was no notable change in melatonin. However, after two hours of light exposure through the iPad, melatonin was drastically inhibited. Blue light has been found to affect teenagers more than adults. Teenagers were more alert and awake compared to adults, even when the teenagers were only exposed to a tenth of the blue light adults were exposed to. In another study, a group of people spent a week outdoor camping without any blue light devices. At the end of the week, the circadian rhythm of the entire group locked into the sunrise and sunset.
A Harvard research study indicated that blood sugar levels and leptin production become altered when the subjects’ schedules were shifted, changing their circadian rhythms. Two additional studies focused on the power of blue light’s powerful suppression of melatonin compared to other light wavelengths. The article concludes with steps to reduce blue light’s negative health effects.
Many people who are convinced they have sleep orders, average over six hours of sleep each night, and our bodies need significantly less sleep than that to remain functional. In fact, one study found that the risk of a stroke was doubled in middle-aged people and older who received more than eight hours of sleep a night. Dr. Irshaad Ebrahim, a director of the Sleep Centre in London believes most people are actually receiving sufficient sleep. Research has showed that the primitive age of ancestral humans actually received only about six hours of sleep each night without any negative impact on their health.
Use of computers and cellphones in the hours immediately before bedtime can lead to fewer hours of deep sleep. Staying up late to study for a test may seem prudent, but research has found the practice can actually impede memory retention. A clinical psychological study found that students who were able to fall asleep earlier and sleep more received better grades than students who slept less. Additionally, as technology continues to grow, the sleep time for students decreases. It has been found that the average American sleeps an hour and a half less than the average sleep time half a century ago.
Alzheimer's disease affects the sleep of people who carry this disease by making it more difficult to fall and stay asleep. An experiment measured the effect of sleep on patients who had Alzheimer's by seeing how well they slept after being exposed to blue light in the evening compared to red light (which is believed not to impact our sleep cycle). In this study, when the patients were exposed to blue light they were able to sleep better throughout the night. In addition, the patients were more active during the day and had more energy when they were exposed to blue light.
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