- Are laser and LED light therapy treatments good for your skin?
- Getting Photodynamic Therapy
- Pros and cons of PDT
- What is PDT used for?
- PDT drugs approved in the US to treat cancer
- Photosensitivity reactions
- Skin changes
- Swelling and pain
- Immune system changes
- Blue light therapy for acne: Benefits, side effects, and costs
- What does the research say?
- How blue light is both bad for you AND good for you! (Huh?)
- What is blue light?
- The perils and benefits of UV
- Key points about blue light
- 1. Blue light is everywhere.
- 2. HEV light rays make the sky look blue.
- 3. The eye is not very good at blocking blue light.
- 4. Blue light exposure may increase the risk of macular degeneration.
- 5. Blue light contributes to digital eye strain.
- 6. Blue light protection may be even more important after cataract surgery.
- 7. Not all blue light is bad.
- Blue light filters and protective eyewear
- Schedule an exam
- Blue light has a dark side
- Light and sleep
- Is nighttime light exposure bad?
- Effects of blue light and sleep
- LED blue light exposure
- Protect yourself from blue light at night
Are laser and LED light therapy treatments good for your skin?
Light can be a powerful tool in skin care, whether it’s an LED facial or a laser treatment for acne.
Light therapy can also seem a little mysterious if you’ve never done it before, because light doesn’t interact with the skin in the same obvious way as, say, a serum or moisturizer.
Here, we’re breaking down the basics of LED and laser skin treatments, explaining what they are, how they work, and experts’ advice for adding them to your skin care routine.
An LED, or light-emitting diode, is basically a special light bulb that only gives off light at a certain wavelength, or color.
These light waves can penetrate deep into the skin and cause reactions within the skin. Different wavelengths produce different results, but the three most popular ones used in skin care are blue, red and near-infrared.
Other colors including green and yellow are sometimes used, but the above three are the most common.
Red light therapy can have numerous benefits, Dr. Joshua Zeichner, director of cosmetic and clinical research in dermatology at New York’s Mount Sinai Hospital, said.
“Red light is anti-inflammatory and has been shown to help stimulate collagen,” Zeichner told TODAY Style in an email. “For this reason, red light may also be used in treating acne, and … it’s commonly used for its anti-aging skin benefits.”
Red light therapy can reduce inflammation and heal damaged skin.Shutterstock
Red and near-infrared light therapy can also help heal damaged or irritated skin. Joanna Vargas, a celebrity esthetician whose clients include Julianne Moore, Constance Wu and Rachel Brosnahan, said she often uses red light therapy to soothe the skin after other treatments.
“I can do a really intense peel on somebody that would normally leave somebody really red for several hours, but after the peel, I can do red and infrared light and you walk out looking a glowing angel,” she told TODAY Style.
Red light therapy is also sometimes used in sports medicine to reduce inflammation and speed up the healing of injuries.
While red light therapy can reduce inflammation, blue light therapy kills bacteria under the skin. This makes it an excellent tool for treating acne, which can be caused by bacteria in the pores.
“NASA paid grants to physicians to study the effects of light on the human body in the late '80s and '90s and what was shown was that when you use blue light, for example, on acne, it's going to kill bacteria even underneath the skin whether you extract it or not,” Vargas said.
“It's an incredible tool for an esthetician because if I’m doing a lot of extractions on somebody, for example, and then we do a mask … I can then put the person under blue light and it will assure me that all the bacteria is gone and that the sites of pimples can heal freely without worrying about getting infections again,” she added.
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Blue light therapy is commonly used as an acne treatment.Shutterstock
Vargas noted that with both blue and red light therapy, it can take a few sessions before you start seeing results.
“I usually tell people that LED light is one of those technologies that you're going to have to trust me for the first three to four sessions,” she said. “And then after the third or fourth one, you're just going to be out living your life, and you'll just start getting compliments on your skin. … I've never had anybody not see a difference.”
LED light therapy is a noninvasive treatment that “can be used across ethnicities and skin types,” Zeichner told TODAY. “I do recommend light therapy as a safe and effective treatment for both acne and aging skin.”
That said, there are certain precautions to keep in mind, said Dr. Paul Jarrod Frank, a celebrity cosmetic dermatologist and founder of PFRANKMD and the PFRANKMD skin salon in New York.
“It’s important to always wear eye shields and not look directly at the lights,” Frank told TODAY Style in an email. “Thirty minutes maximum is recommended for treatment and no more than two times per week.”
Vargas also cautioned that you can’t do LED light treatments while pregnant, if you have a pacemaker or if you’re on certain medications.
Bottom line: always check with your dermatologist before beginning light therapy treatments.
A number of at-home LED light therapy tools have come on the market in recent years, including masks, panels and handheld devices. Are these as safe and effective as treatments from a dermatologist or esthetician?
It depends, Vargas said.
“I think not all things are created equal,” she told TODAY Style. “I feel more comfortable when clients purchase at-home devices where the company has shared the amount of LED lights in the device, what's the exact penetration and saturation level of the skin. When companies don't make that as clear, it's a little harder to tell if something's going to work or not work.”
Besides possibly not working as well, some at-home devices could actually damage the skin, Vargas said.
“I have had clients purchase at-home devices that created melasma (a pigmentation disorder) because they weren't quite as good as they thought they were,” she said. “So you just have to be sort of mindful of what brand you're buying and make sure that it's something that is actually effective.”
LED therapy, laser treatments involve light interacting with the skin. However, lasers use a much higher-energy, targeted beam of light.
“Lasers are fancy knives,” Frank told TODAY Style. “They use a source of light, of various wavelengths, to target certain areas, while not harming other areas.”
Laser treatments are often used to treat acne and rosacea. Lasers can reduce redness associated with both conditions, and for people with rosacea, lasers can reduce the appearance of tiny blood vessels on the face.
Other common uses for lasers include removing the appearance of sun damage, hyperpigmentation, broken capillaries and acne scars.
Certain types of lasers are also great for skin tightening or resurfacing.
“Resurfacing lasers target water in the skin,” Zeichner said. “They work by creating microscopic damage to the skin and allowing it to heal itself up in a more cosmetically appealing manner.”
People with a history of eczema, psoriasis or any type of skin disease should check with a dermatologist before using lasers, Frank said.
Lasers should also not be used on people who have recently been exposed to ultraviolet radiation without protection, according to the American Academy of Dermatology. So, if you’re planning on getting a laser treatment, always wear sunscreen and avoid tanning beds (which is good skin care advice in general).
Also, because laser treatments are more intense on the skin than LED therapy, there’s the risk of developing dark or light spots, or even scars, if you're not working with an experienced practitioner.
“Make sure that you are being treated by an appropriately trained medical professional, a board-certified dermatologist with expertise in use of lasers,” Zeichner recommended.
Frank agreed that lasers can be “risky” if used incorrectly, and he recommended that people only do laser treatments with qualified experts.
When used correctly, lasers are a powerful skin care treatment, Frank said.
“No one above the age of 25 can’t benefit from some degree of a laser. It is safe, versatile and, when used in experienced hands, extremely effective,” he told TODAY Style. “It removes sun damage, builds and remodels collagen and decreases the risk of common skin cancer — and it makes you look great. It is the most valuable tool in my practice.”
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Getting Photodynamic Therapy
Photodynamic therapy (PDT) is a treatment that uses special drugs, sometimes called photosensitizing agents,along with light to kill cancer cells. The drugs only work after they have been activated or “turned on” by certain kinds of light. PDT may also be called photoradiation therapy, phototherapy, or photochemotherapy.
Depending on the part of the body being treated, the photosensitizing agent is either put into the bloodstream through a vein or put on the skin. Over a certain amount of time the drug is absorbed by the cancer cells.
Then light is applied to the area to be treated. The light causes the drug to react and form a special kind of oxygen molecule that kills the cells.
PDT might also help by destroying the blood vessels that feed the cancer cells and by alerting the immune system to attack the cancer.
The period of time between when the drug is given and when the light is applied is called the drug-to-light interval. It can be anywhere from a couple of hours to a couple of days, depending on the drug used.
The light used in PDT comes from certain kinds of lasers or from light-emitting diodes (LEDs). The kind of light used depends on the type of cancer and where it is located in the body. PDT is usually done as an outpatient procedure (meaning you won't have to stay in the hospital) but is sometimes combined with surgery, chemotherapy or other anti-cancer drugs, or radiation therapy.
Pros and cons of PDT
Studies have shown that PDT can work as well as surgery or radiation therapy in treating certain kinds of cancers and pre-cancers. It has some advantages, such as:
- It has no long-term side effects when used properly.
- It’s less invasive than surgery.
- It usually takes only a short time and is most often done as an outpatient procedure.
- It can be targeted very precisely.
- Un radiation, PDT can be repeated many times at the same site if needed.
- There’s usually little or no scarring after the site heals.
- It often costs less than other cancer treatments.
But PDT has limits, too:
- PDT can only treat areas where light can reach. This means it’s mainly used to treat problems on or just under the skin, or in the lining of organs that can be reached with a light source. Because light can’t travel very far through body tissues, PDT can’t be used to treat large cancers or cancers that have grown deeply into the skin or other organs.
- PDT can’t be used to treat cancers that have spread to many places.
- The drugs used for PDT leave people very sensitive to light for some time, so special precautions must be taken after the drugs are put in or on the body.
- PDT can’t be used in people who have certain blood diseases.
What is PDT used for?
PDT can be used in people with certain types of cancer to help them live longer and improve their quality of life. It’s becoming more widely recognized as a valuable treatment option for certain types of localized cancers (cancers that have not spread far from where they started).
PDT drugs approved in the US to treat cancer
Several photosensitizing agents are currently approved by the US Food and Drug Administration (FDA) to treat certain cancers or pre-cancers. Here are two of the most widely used:
- Porfimer sodium (Photofrin) is a very widely used and studied photosensitizer. It’s activated by red light from a laser. It’s approved by the FDA to treat patients with certain kinds of cancers of the esophagus and lung, and is being studies in other types of cancer.
- Aminolevulinic acid (ALA or Levulan) is a drug that’s put right on the skin. It’s used to treat actinic keratosis (AK), a skin condition that can become cancer, and is used only on the face or scalp. A special blue light, rather than laser light, is used to activate this drug.
Researchers are always looking for new PDT drugs, and new ways to give them. PDT is also being combined with other types of treatment, such surgery and radiation therapy. Future possibilities include other combination treatments with PDT drugs, as well as new PDT drugs that can target tumor cells better, can leave normal cells more quickly, and allow the treatment light to penetrate deeper.
The most common side effect of PDT is sensitivity to bright lights and sunlight. These reactions caused by PDT light can show up on the skin where the drug is applied. They usually involve redness and a tingling or burning sensation. For a period of time after treatment, you'll need to be careful to not expose treated areas of your face and scalp to light.
- Stay strong, direct light.
- Stay indoors as much as possible.
- Wear protective clothing and wide-brimmed hats to avoid sunlight when outdoors.
- Avoid beaches, snow, light colored concrete, or other surfaces where strong light may be reflected.
Sunscreens will not protect the skin from photosensitivity reactions.
Depending on the type and location of treatment, the treated skin might turn red and may swell for a period of time. With some treatments, blisters may form. This may last hours to days after treatment. The skin may also have a burning sensation or may be itchy or change color after treatment.
Swelling and pain
Swelling in the treated area can lead to pain and problems with the tissues and organs working properly. Be sure to ask your doctor which side effects you might expect and which you need to report right away. Get the phone number to call if you have problems after regular office hours.
Immune system changes
Sometimes PDT treatments can make the immune system work differently, usually by stimulating it to work more. Sometimes it can become weaker for period of time. In very rare cases, PDT can cause skin cancer at the site where treatment was given. Some researchers believe this happens if the immune system is weakened by PDT.
Blue light therapy for acne: Benefits, side effects, and costs
Blue light therapy is a noninvasive treatment for acne that uses light to kill certain bacteria on the skin.
A form of phototherapy, blue light treatments are FDA-approved for acne vulgaris that is moderate or has not responded to other therapies.
Blue light therapy can be carried out in a dermatologist’s office or at home.
- Blue light therapy uses light in the blue wavelength range to kill the bacteria Propionibacterium acnes, or P. acnes, on the skin.
- There is no recovery time, and the treatment has relatively few, if any, adverse effects.
- Studies show moderate evidence for the efficacy of blue light treatments for people with mild to moderate acne.
- It should be noted that most studies on blue light therapy are small and do not report on long-term results. There is a lack of data for outcomes in cases of severe acne.
Share on PinterestBlue light has a frequency that can kill P. acnes bacteria and treat acne.
According to the American Academy of Dermatology, light therapies “show great promise in treating acne,” with many people experiencing a significant improvement in their skin health after a number of sessions.
Blue light therapy can be used to treat acne that is already present on the skin or to control the condition before an outbreak occurs.
However, the academy warns that acne does not usually completely clear up with phototherapy alone.
Additional treatments are often needed to manage acne symptoms fully.
What does the research say?
Findings that support the effects of blue light therapy for acne include:
- A study on people with mild to moderate acne who were treated with blue light therapy twice weekly for 5 weeks reported that lesions were reduced by 64 percent.
- A 2004 study on 28 adults with facial acne who underwent 8 sessions of blue light therapy over 4 weeks experienced nearly 65 percent improvement in acne lesions overall.
- A Japanese study of 10 people with acne on their face or back reported that targeted blue light therapy once or twice a week led to a significant reduction in acne severity in eight participants. None experienced any harmful effects.
- In another study, 33 people with mild to moderate facial acne self-administered blue light application twice daily for 8 weeks, along with certain skincare products. At the end, over 90 percent of participants reported improvements in overall skin appearance, clarity, tone, texture, and smoothness. The vast majority, 82 percent, were satisfied with the treatment system, and 86 percent reported that it was gentler than other acne treatments.
It is important to note that the majority of this research involves self-reported outcomes, which may be less reliable than using the results of clinical tests.
Blue light therapy may offer some benefits over alternative acne treatments, as it is considered:
- safe and gentle
- appropriate for all areas of the body
- suitable for use with most other acne therapies
Un photodynamic therapy, there is no requirement to avoid the sun following treatment. Blue light therapy does not cause any scarring.
A number of other conditions can be treated with blue light therapy, including:
- skin cancer
- skin problems
- mood disorders
- sleep disorders
Blue light therapy can be administered in a dermatologist’s office or at home.
In-office treatments are usually carried out 8 times over a 4-week period. Each session lasts 15-30 minutes, depending on the severity of the acne and the size of the area of the body being treated.
It is advisable to arrive at the doctor’s office before treatment with clean, makeup-free skin. The doctor will provide goggles to protect the eyes while the patient lies or sits under a blue light for the duration of the treatment. Most people do not experience any pain or discomfort.
Following treatment, some inflammation and redness may be noticeable around the treated area, although this should resolve quickly. Makeup can usually be applied immediately, although people should follow their doctor’s advice on this.
Results are noticeable within 2-4 weeks, or even sooner in some cases.
Between treatments, people should avoid touching or picking the blemishes on their skin. It is important to follow the dermatologist’s advice on the use of products and home care techniques, during and after the treatments.
Follow-up sessions are usually required to maintain results.
When used correctly, blue light therapy does not appear to pose any serious long-term effects. However, some minor adverse reactions may be experienced, such as:
People with the rare condition known as porphyria, which is a blood disorder that causes increased sensitivity to light, should avoid blue light therapy. Similarly, it should not be used by people with lupus and allergies to porphyrins.
In recent years, a growing number of blue light products have become available to treat acne at home.
These are less aggressive than in-office treatments but may be more convenient and cost-effective for some users.
Self-applied blue light treatment has been reported to be easy and safe to use.
In general, blue light therapy costs between $40-$60 per session. Most insurance plans do not cover light therapy treatment for acne.
At-home devices may be an alternative option, particularly for those with mild acne. Blue light wands and masks can be purchased for as little as $35. It is important to follow the manufacturer’s instructions when using these products.
How blue light is both bad for you AND good for you! (Huh?)
Visible light is much more complex than you might think.
Stepping outdoors into sunlight; flipping on a wall switch indoors; turning on your computer, phone or other digital device — all of these things result in your eyes being exposed to a variety of visible (and sometimes invisible) light rays that can have a range of effects.
Most people are aware that sunlight contains visible light rays and also invisible ultraviolet rays that can tan or burn the skin. But what many don't know is that the visible light emitted by the sun comprises a range of different-colored light rays that contain different amounts of energy.
What is blue light?
Sunlight contains red, orange, yellow, green and blue light rays and many shades of each of these colors, depending on the energy and wavelength of the individual rays (also called electromagnetic radiation). Combined, this spectrum of colored light rays creates what we call “white light” or sunlight.
The light spectrum
Without getting into complicated physics, there is an inverse relationship between the wavelength of light rays and the amount of energy they contain. Light rays that have relatively long wavelengths contain less energy, and those with short wavelengths have more energy.
Rays on the red end of the visible light spectrum have longer wavelengths and, therefore, less energy. Rays on the blue end of the spectrum have shorter wavelengths and more energy.
The electromagnetic rays just beyond the red end of the visible light spectrum are called infrared — they are warming, but invisible. (The “warming lamps” you see keeping food warm at your local eatery emit infrared radiation. But these lamps also emit visible red light so people know they are on! The same is true for other types of heat lamps.)
On the other end of the visible light spectrum, blue light rays with the shortest wavelengths (and highest energy) are sometimes called blue-violet or violet light. This is why the invisible electromagnetic rays just beyond the visible light spectrum are called ultraviolet (UV) radiation.
The perils and benefits of UV
UV rays have higher energy than visible light rays, which makes them capable of producing changes in the skin that create a suntan. In fact, the bulbs in tanning booths emit a controlled amount of UV radiation specifically for this reason.
But too much exposure to UV causes a painful sunburn — and even worse, can lead to skin cancer. These rays also can cause sunburned eyes — a condition called photokeratitis or snow blindness.
But ultraviolet radiation, in moderation, also has beneficial effects, such as helping the body manufacture adequate amounts of vitamin D.
Generally, scientists say the visible light spectrum comprises electromagnetic radiation with wavelengths ranging from 380 nanometers (nm) on the blue end of the spectrum to about 700 nm on the red end. (By the way, a nanometer is one billionth of a meter — that's 0.000000001 meter!)
Blue light generally is defined as visible light ranging from 380 to 500 nm. Blue light sometimes is further broken down into blue-violet light (roughly 380 to 450 nm) and blue-turquoise light (roughly 450 to 500 nm).
So approximately one-third of all visible light is considered high-energy visible (HEV) or “blue” light.
Key points about blue light
ultraviolet radiation, visible blue light — the portion of the visible light spectrum with the shortest wavelengths and highest energy — has both benefits and dangers. Here are important things you should know about blue light:
1. Blue light is everywhere.
Sunlight is the main source of blue light, and being outdoors during daylight is where most of us get most of our exposure to it. But there are also many man-made, indoor sources of blue light, including fluorescent and LED lighting and flat-screen televisions.
Most notably, the display screens of computers, electronic notebooks, smartphones and other digital devices emit significant amounts of blue light.
The amount of HEV light these devices emit is only a fraction of that emitted by the sun. But the amount of time people spend using these devices and the proximity of these screens to the user's face have many eye doctors and other health care professionals concerned about possible long-term effects of blue light on eye health.
2. HEV light rays make the sky look blue.
The short-wavelength, high-energy light rays on the blue end of the visible light spectrum scatter more easily than other visible light rays when they strike air and water molecules in the atmosphere. The higher degree of scattering of these rays is what makes a cloudless sky look blue.
3. The eye is not very good at blocking blue light.
Anterior structures of the adult human eye (the cornea and ) are very effective at blocking UV rays from reaching the light-sensitive retina at the back of the eyeball. In fact, less than one percent of UV radiation from the sun reaches the retina, even if you aren't wearing sunglasses.
(Keep in mind, though, that sunglasses that block 100 percent of UV are essential to protect these and other parts of the eye from damage that could lead to cataracts, snow blindness, a pinguecula and/or pterygium, and even cancer.)
On the other hand, virtually all visible blue light passes through the cornea and lens and reaches the retina.
4. Blue light exposure may increase the risk of macular degeneration.
The fact that blue light penetrates all the way to the retina (the inner lining of the back of the eye) is important, because laboratory studies have shown that too much exposure to blue light can damage light-sensitive cells in the retina.
This causes changes that resemble those of macular degeneration, which can lead to permanent vision loss.
Although more research is needed to determine how much natural and man-made blue light is “too much blue light” for the retina, many eye care providers are concerned that the added blue light exposure from computer screens, smartphones and other digital devices might increase a person's risk of macular degeneration later in life.
5. Blue light contributes to digital eye strain.
Because short-wavelength, high energy blue light scatters more easily than other visible light, it is not as easily focused. When you're looking at computer screens and other digital devices that emit significant amounts of blue light, this unfocused visual “noise” reduces contrast and can contribute to digital eye strain.
Research has shown that lenses that block blue light with wavelengths less than 450 nm (blue-violet light) increase contrast significantly. Therefore, computer glasses with yellow-tinted lenses may increase comfort when you're viewing digital devices for extended periods of time.
6. Blue light protection may be even more important after cataract surgery.
The lens in the adult human eye blocks nearly 100 percent of the sun's UV rays. As part of the normal aging process, the eye's natural lens eventually blocks some short-wavelength blue light as well — the type of blue light most ly to cause damage to the retina and lead to macular degeneration and vision loss.
If you have cataracts and are about to have cataract surgery, ask your surgeon what type of intraocular lens (IOL) will be used to replace your cloudy natural lens, and how much blue light protection the IOL provides.
After cataract surgery you might benefit from eyeglasses that have lenses with a special blue light filter — especially if you spend long hours in front of a computer screen or using other digital devices.
7. Not all blue light is bad.
So, is all blue light bad for you? Why not block all blue light, all the time?
Bad idea. It's well documented that some blue light exposure is essential for good health. Research has shown that high-energy visible light boosts alertness, helps memory and cognitive function and elevates mood.
In fact, something called light therapy is used to treat seasonal affective disorder (SAD) — a type of depression that's related to changes in seasons, with symptoms usually beginning in the fall and continuing through winter.
The light sources for this therapy emit bright white light that contains a significant amount of HEV blue light rays.
Also, blue light is very important in regulating circadian rhythm — the body's natural wakefulness and sleep cycle. Exposure to blue light during daytime hours helps maintain a healthful circadian rhythm.
But too much blue light late at night (reading a novel on a tablet computer or e-reader at bedtime, for example) can disrupt this cycle, potentially causing sleepless nights and daytime fatigue.
Blue light filters and protective eyewear
If you are using your phone constantly — especially if you use it primarily for texting, e-mailing and web browsing — a convenient way to reduce your blue light exposure is to use a blue light filter.
Digital electronic devices emit blue light that can cause eye strain and may lead to eye problems over time.
These filters are available for smartphones, tablets, and computer screens and prevent significant amounts of blue light emitted from these devices from reaching your eyes without affecting the visibility of the display. Some are made with thin tempered glass that also protects your device's screen from scratches.
Examples of blue light filters for digital devices include: Eyesafe (Health-E), iLLumiShield, RetinaShield (Tech Armor), Retina Armor (Tektide), Frabicon and Cyxus.
As mentioned above, computer glasses also can be helpful to reduce blue light exposure from computers and other digital devices. These special-purpose glasses are available without an eyeglass prescription if you have no need for vision correction or if you routinely wear contact lenses to correct your eyesight.
Or computer glasses can be specially prescribed to optimize your vision specifically for the distance from which you view your devices.
If you have presbyopia and routinely wear progressive lenses or bifocals, prescription computer glasses with lenses give you the additional benefit of a much larger field of view for seeing your entire computer screen clearly. (Keep in mind, though, that this type of computer eyewear is exclusively for seeing objects within arm's length and cannot be worn for driving or other distance vision needs.)
Also, a number of lens manufacturers have introduced special glare-reducing anti-reflective coatings that also block blue light from both natural sunlight and digital devices.
You also may want to consider photochromic lenses, which provide seamless protection from UV and blue light both indoors and out and also automatically darken in response to UV rays outdoors to increase comfort and reduce glare.
Ask your eye doctor or optician which type of vision correction and lens features best suit your needs for viewing your computer and other digital devices and protecting your eyes from blue light.
Worried about blue light? Find an optical shop near you or online and shop for blue-light blocking glasses and sunglasses.
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Gary Heiting, OD
Gary Heiting, OD, is a former senior editor of AllAboutVision.com. Dr. Heiting has more than 30 years of experience as an eye care provider, health educator and consultant to the eyewear … read more
The lowdown on blue light: good vs. bad, and its connection to AMD. Review of Optometry. February 2014.
The role of UV damage in ocular disease. Review of Optometry. October 2012.
The contrast sensitivity function measured under blue haze conditions. Investigative Ophthalmology & Visual Science. March 2012.
Retinal light toxicity. Eye. January 2011.
Superior short-wavelength contrast sensitivity in asthenopics during reflexive readjustments of ocular accommodation. Ophthalmic & Physiological Optics. July 2007.
Contrast is enhanced by yellow lenses because of selective reduction of short-wavelength light. Optometry and Vision Science. February 2000.
Blue light has a dark side
Although it is environmentally friendly, blue light can affect your sleep and potentially cause disease. Until the advent of artificial lighting, the sun was the major source of lighting, and people spent their evenings in (relative) darkness. Now, in much of the world, evenings are illuminated, and we take our easy access to all those lumens pretty much for granted.
But we may be paying a price for basking in all that light. At night, light throws the body's biological clock—the circadian rhythm— whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.
Light and sleep
Everyone has slightly different circadian rhythms, but the average length is 24 and one-quarter hours. The circadian rhythm of people who stay up late is slightly longer, while the rhythms of earlier birds fall short of 24 hours. Dr. Charles Czeisler of Harvard Medical School showed, in 1981, that daylight keeps a person's internal clock aligned with the environment.
Is nighttime light exposure bad?
Some studies suggest a link between exposure to light at night, such as working the night shift, to some types of cancer, diabetes, heart disease, and obesity.
That's not proof that nighttime light exposure causes these conditions; nor is it clear why it could be bad for us.
But we do know that exposure to light suppresses the secretion of melatonin, a hormone that influences circadian rhythms, and there's some experimental evidence (it's very preliminary) that lower melatonin levels might explain the association with cancer.
A Harvard study shed a little bit of light on the possible connection to diabetes and possibly obesity. The researchers put 10 people on a schedule that gradually shifted the timing of their circadian rhythms. Their blood sugar levels increased, throwing them into a prediabetic state, and levels of leptin, a hormone that leaves people feeling full after a meal, went down.
Even dim light can interfere with a person's circadian rhythm and melatonin secretion.
A mere eight lux—a level of brightness exceeded by most table lamps and about twice that of a night light—has an effect, notes Stephen Lockley, a Harvard sleep researcher.
Light at night is part of the reason so many people don't get enough sleep, says Lockley, and researchers have linked short sleep to increased risk for depression, as well as diabetes and cardiovascular problems.
Effects of blue light and sleep
While light of any kind can suppress the secretion of melatonin, blue light at night 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.
In another study of blue light, researchers at the University of Toronto compared the melatonin levels of people exposed to bright indoor light who were wearing blue-light–blocking goggles to people exposed to regular dim light without wearing goggles.
The fact that the levels of the hormone were about the same in the two groups strengthens the hypothesis that blue light is a potent suppressor of melatonin. It also suggests that shift workers and night owls could perhaps protect themselves if they wore eyewear that blocks blue light.
Inexpensive sunglasses with orange-tinted lenses block blue light, but they also block other colors, so they're not suitable for use indoors at night. Glasses that block out only blue light can cost up to $80.
LED blue light exposure
If blue light does have adverse health effects, then environmental concerns, and the quest for energy-efficient lighting, could be at odds with personal health. Those curlicue compact fluorescent lightbulbs and LED lights are much more energy-efficient than the old-fashioned incandescent lightbulbs we grew up with. But they also tend to produce more blue light.
The physics of fluorescent lights can't be changed, but coatings inside the bulbs can be so they produce a warmer, less blue light.
LED lights are more efficient than fluorescent lights, but they also produce a fair amount of light in the blue spectrum.
Richard Hansler, a light researcher at John Carroll University in Cleveland, notes that ordinary incandescent lights also produce some blue light, although less than most fluorescent lightbulbs.
Protect yourself from blue light at night
Use dim red lights for night lights. Red light has the least power to shift circadian rhythm and suppress melatonin.
Avoid looking at bright screens beginning two to three hours before bed.
If you work a night shift or use a lot of electronic devices at night, consider wearing blue-blocking glasses or installing an app that filters the blue/green wavelength at night.
Expose yourself to lots of bright light during the day, which will boost your ability to sleep at night, as well as your mood and alertness during daylight.
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