BLUE LIGHT

1. BLUE LIGHT: IT'S BOTH BAD
AND GOOD FOR YOU
OPTOM FASLU MUHAMMED

2.  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.

3. 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.
 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.

4.  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.

6. 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 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.

7.  Blue light contributes to digital eye strain; computer
glasses that block blue light may increase comfort.
 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.

8. KEY POINTS ABOUT BLUE LIGHT
 Like 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:

9. 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, smart phones 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.

10. 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.

11. THE EYE IS NOT VERY GOOD AT
BLOCKING BLUE LIGHT.
 Anterior structures of the adult
human eye (the cornea and lens) 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.

12. 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, smart phones and other digital
devices might increase a person's risk of macular
degeneration later in life.

13. 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.

14. 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 likely 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.

15. 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.

16. 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.
 These filters are available for smart phones, 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, Retina Shield (Tech
Armor), Retina Armor (Tektide), Frabicon and Cyxus.

17.  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 they
 can be specially prescribed to optimize your vision
specifically for the distance from which you view your
devices.

18.  If you have presbyopia and routinely wear progressive
lenses or bifocals, prescription computer glasses with single
vision 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.