What is Blue Light?
Light is electromagnetic radiation of a variety of wavelengths within the electromagnetic spectrum.
There is both visible and non-visible light. Non-visible light includes ultraviolet (UV) and infrared light, while visible light includes the whole spectrum of the rainbow, including blue light. Within the visible light spectrum, each wavelength is represented by a color.
Of all the colors of the visible light spectrum, blue light (wavelength 446 – 477 nm) has the strongest impact on physiology and circadian rhythm because our pigments react to this wavelength [1, 2, 3].
Humans have evolved to rise with the sun and go to sleep after sunset. Before the advent of technology, humans only used sources that emitted yellow, orange, and red light, such as fire, candles, and lamps. These lights have much less impact on our circadian rhythm and sleep-wake cycles than blue light.
Nowadays, advances in lighting and other technologies like television, computers, and digital clocks among others, have introduced more blue-white light to our environment. In addition, these lights are available at all hours, which can affect our health and wellbeing.
The higher efficiency “green” light bulbs are not necessarily as beneficial for humans as they supposedly are for the earth. Compact fluorescent light (CFL) bulbs contain about 25% and LEDs about 35% of blue light.
Generally, blue light is beneficial during the day, but harmful at night.
What are the Physiological Effects of Blue Light?
Light exposure anchors human body functions to the rise and fall of the sun. When sunlight, which contains blue light, hits the retina, the photoreceptor cells transmit the nerve impulses to the hypothalamus. The hypothalamus is the command central for hunger, thirst, temperature regulation, hormone secretion, and sleep patterns, which fluctuate according to our circadian rhythm.
When light hits the eye, it hits the retina. The light-sensitive retina is actually considered part of the central nervous system (CNS) and is connected to the brain via the optic nerve. There are several layers of nerve cells in the retina, but the ones that are sensitive to light are the photoreceptor cells. Rods and cones are the light sensing cells that allow us to see, while the light-sensitive retinal ganglion cells are important for circadian rhythm entrainment.
The suprachiasmatic nucleus (SCN) in the hypothalamus coordinates light exposure with bodily functions through hormonal, autonomic (involuntary nerve impulses), and feeding-related cues .
Blue Light at Night Disrupts Your Body’s Circadian Rhythm
Intrinsically photosensitive retinal ganglion cells contain melanopsin (a light sensor protein), whose job is to synchronize the body’s circadian clock to light .
Exposure to blue light at night signals your body that it is daytime, consequently, messing up your circadian rhythm, which is crucial to many body processes.
1) Lowers Melatonin Production
Melatonin is an important hormone that controls the sleep-wake cycle .
Even dim light can interfere with a person’s circadian rhythm and melatonin secretion. A mere 8 lux (double the brightness of a night light) can inhibit melatonin .
The brighter the light and the longer the exposure time, the less melatonin the eye cells produce .
A theoretical model of different types of light and exposures indicates the following for melatonin suppression :
- Monochromatic red light at 100 lux, a reasonable living room lighting level, would take 403 hours of exposure to suppress melatonin by 50%
- Candle – 66 min suppresses melatonin by 50%
- 60-watt incandescent bulb – 39 min suppresses melatonin by 50%
- 58-watt deluxe daylight fluorescent light – 15 min suppresses melatonin by 50%
- Pure white high-output LED – 13 min suppresses melatonin by 50%
For example, after 1 hr of light at midnight, melatonin could be suppressed up to 71%, 67%, 44%, 38%, and 16% with intensities of 3,000, 1,000, 500, 350, and 200 lux, respectively .
Melatonin levels are reduced most with dilated pupils exposed to 90 min of monochromatic blue light from 2:00 to 3:30 AM at a brightness of 0.1 lux, which is equivalent to the light of a full moon .
Blue light, even at a dim, moonlight level (0.1 lux), suppressed melatonin production more than any other wavelength .
People with light-colored eyes (blue or green, for example) are more susceptible to melatonin suppression by blue light than those with darker eyes .
2) Can Raise Cortisol
3) May Suppress alpha-MSH Release
4) Worsens Sleep Quality
Nighttime blue light exposure can:
- Increase the time it takes to fall asleep 
- Reduce total and deep sleep duration 
- Reduce overall sleep quality 
- Reduce melatonin effects, such as increased deep sleep in elderly insomniacs and increased REM sleep in people with reduced REM 
Artificial Light Exposure At Night Worsens Metabolic Health
5) Can Cause Weight Gain
In a questionnaire-based study on 100,000 women in the UK, obesity parameters (BMI, waist:hip ratio, waist:height ratio, and waist circumference) were significantly associated with increased exposure to light at night .
Mice exposed to dim (5 lux) light at night have altered core circadian clock rhythms in the hypothalamus, which resulted in increased body mass compared to mice that were not exposed to light, even though they ate the same amount of food .
The hypothalamus contains high concentrations of receptors for both leptin, the satiating hormone, and ghrelin, the appetite-stimulating hormone. Exposure to light has been found to alter the secretions of these hormones, increasing hunger and decreasing satiety , which can lead to weight gain.
6) Can Raise the Risk for Diabetes
Artificial blue light alters blood sugar metabolism .
Light at night disrupts the circadian clock of pancreatic islet cells and β-cell function in cell studies. This impaired circadian clock may be responsible for altered islet function and survival and, consequently, an increased risk of type 2 diabetes .
In mice, dim light at night brings on metabolic syndrome symptoms, which can be reversed by returning to complete darkness at night .
7) Can Raise the Risk for Heart Disease
Blue light disrupts the circadian rhythm in heart muscle cells, thus putting the heart out of synch and increasing the risk of high blood pressure, insulin resistance, and cardiovascular disease .
Its inhibition of melatonin synthesis leads to increased inflammation, increased blood pressure, high LDL and total cholesterol, decreased antioxidant capacity, and overall elevated risk of cardiovascular disease .
Blue Light At Night May Damage the Eyes
Blue light exposure can lead to macular degeneration in animals .
In albino mice, blue light caused cell death in the retina, while green light did not .
Blue light causes:
- reduced melanin (not to be confused with melatonin, melanin is a pigment with antioxidant properties that can prevent eye damage) in the retina .
- the destruction of the fatty acid DHA in the retina .
- increased free radicals in the presence of oxygen around the retina, leading to the breakdown of the retinal pigment epithelium (cells that line the epithelium) .
In eyes that are undergoing age-related macular degeneration, the damaged cells release VEGF, which can induce new blood vessel formation . These new blood vessels are fragile and can easily burst to lead to blood leaking out and damaging the back of the eye where light is transformed into a picture .
9) Can Contribute to Glaucoma
The suppression of melatonin by blue light may cause glaucoma .
In glaucoma patients, functional retinal ganglion cells are more susceptible to the damaging effects of blue light . In addition, the function of these cells decreases as the disease progresses .
Therefore, filtering out the blue light from entering the eyes may be beneficial for the treatment of glaucoma .
Other Chronic Diseases Linked to Blue Light Exposure at Night
10) May Contribute to Depression
In an animal model of obstructive sleep apnea, dim light at night increased depressive behaviors .
A study of 500 elderly individuals (average age 72.8) discovered that exposure to light at night is significantly associated with depression .
Another study of 1,100 elderly people found that lowered melatonin levels and higher nighttime light intensity were associated with depression .
11) Blue Light at Night Can Increase Cancer Risk
As having lowered melatonin levels is associated with an increased risk of cancer, and blue light prevents melatonin production, blue light exposure at night may increase the risk of cancer, and blocking blue light may be helpful in preventing it .
However, studies on the effect of shift work -with the associated nighttime exposure to light- on various cancers (breast, prostate, colorectal, and lymphoma) showed inconsistent results .
In a study of over 50,000 women, long-term shift work, which lowers melatonin levels, was significantly associated with an increased risk of endometrial cancer .
The strongest association was between shift work (representing light at night) and breast cancer .
Numerous studies show that lowered melatonin due to nighttime light exposure is a risk factor for breast cancer .
Women who are blind are half as likely to get breast cancer as those who are not blind .
A global study in 2016 on artificial light at night (ALAN) and cancer in 158 countries found a significant correlation between ALAN and all forms of cancer, as well as lung, breast, colorectal, and prostate cancers individually .
Benefits of Blue Light Exposure During the Day
1) Exposure During the Day Can Help to Sleep at Night
Combining a breakfast rich in tryptophan with blue light exposure during the day may induce melatonin secretion and quality sleep at night .
In people over 60 years old, bright light therapy during the day improve insomnia. Forty-five minutes of light therapy was more effective than 20 minutes .
2) May Help Treat Acne
Blue light inhibits the growth of Propionibacterium acnes, a bacteria that causes acne. Daily blue light treatments for mild-to-moderate inflammatory acne significantly reduced the number of acne lesions [60, 61].
In a study on 30 patients using blue light LED treatments for acne at home, the blue light therapy required less time to improve the condition than the sham treatment .
3) Helps to Alleviate Seasonal Affective Disorder
4) May Improve Neurodegenerative Disease
In Parkinson’s, light exposure (1,000 – 1,500 lux, 1 hour daily for 2 weeks) improved the mood, social behavior, and motor function and, in some cases, even reduced dopamine replacement by 13% – 100% .
5) May Promote Healing
6) Could Help to Slow Down Cancer Growth
In animals, daytime blue light exposure was helpful for raising melatonin at night, which significantly slows down prostate cancer growth .
7) May Stimulate Reproductive Hormones in Women
How to Use Blue Light Exposure to Your Advantage
1) Get Plenty of Sunlight During the Day
Getting more bright light during the day lessens your sensitivity to light in the evening as well as melatonin suppression by nighttime light exposure .
You can use this bright light device in the morning about 1 foot away from your eyes, or this portable bright light device.
If you work in an office and can’t get the big one, then I’d recommend the following instead. When I can’t be around my computer or bright light device, I use a bright light device that you can put on a cap. I use this EMF cap with it. You should use the bright light first thing in the morning to reset your circadian rhythm. I recommend 15 minutes of use if you’re sensitive to bright light and 30 minutes if you aren’t.
2) Use Blue Blocking Glasses After Sunset
Red or amber colored glasses block blue light from entering your eyes. UVEX glasses will only block out blue light. You want to start wearing these glasses 4 hours before you go to sleep. These Swanick glasses are better for social settings.
3) Use Blue Blocking or Red Light Bulbs
Switching from regular light bulbs to blue blocking or red light bulbs can reduce blue light exposure.
4) Install the F.lux program on Your Computer and Tablet
Computers, iPads, smartphones and other digital devices emit blue light. You can reduce the flue light by installing F.lux and using a blue light filter app on your smartphones. You can also use blue blocking red sheets to cover your iPad or other screens.
In addition to cutting blue light out at night, you should dim all your light-emitting devices to the lowest setting.
5) Sleep in total darkness
Buy blackout curtains for your windows and black tape for blue-emitting electronics.
6) Removing Glasses or Contacts When You’re Outside
Glasses and contact lenses filter out UV lights. UV light should directly hit your eyes to have an effect on your circadian rhythm.
7) Supplementation with Lutein and Zeaxanthin
Take supplements with lutein and zeaxanthin, which may reduce the oxidative effects of blue light .
Genes that Affect Susceptibility to Blue Light at Night
In a study on Norwegian shift-working women, TT carriers for CLOCK allele rs3749474 had a lower risk of breast cancer compared to the other shift workers, indicating that they were less negatively impacted by nightlight .
In the same study, GG carriers for CLOCK rs11133373 had an increased risk of breast cancer, indicating that they were more negatively impacted by nightlight .
Again in the study of Norwegian shift-working women, TT carriers for BMAL1/ARNTL rs2278749 had a reduced risk of breast cancer compared to the other shift workers, indicating they were less negatively impacted by nightlight .
Women with the highest number of successive night shifts and carrying at least one variant allele of SNPs in the two core circadian genes BMAL1/ARNTL (rs2290035, rs969485) and ROR-b (rs3903529, rs3750420) had an increased risk of breast cancer .
In AANAT, a gene controlling melatonin production, CC carriers for rs4238989 had an increased risk of breast cancer associated with light exposure at night, whereas GG carriers for rs3760138 had a higher risk of breast cancer (40%) with the highest (4 shifts) light exposure at night .
The SCN in the hypothalamus is a central command for sleep patterns or circadian rhythm entrainment. It is connected to the retina via the retinohypothalamic (RHT) tract. You can read more about the SCN’s involvement in the circadian rhythm here. The photopigment melanopsin, contained in the intrinsically photosensitive retinal ganglion cells of the eye, acts as an information gatherer/communicator. Melanopsin determines the body’s reflexive response to light such as pupil size change and release of melatonin from the pineal gland.
Internal body clocks are created through regulation of the genes CLOCK, ARNTL, and PER3 in neurons. These are adjusted by light input from the photoreceptors. Read How Your Genetics Affect Sleep for a more detailed description.
Want More Targeted Ways to Improve Your Sleep?
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