“Even under extreme long-term viewing conditions, none of the low
energy light bulbs, computers, tablets and mobile phones we assessed
suggested cause for concern for public health,” said lead author
John O’Hagan, head of the Laser and Optical Radiation Dosimetry
Group of Public Health England in Chilton, U.K.
As people are using computers and phones more often and low-energy
lighting like fluorescent and LED bulbs is becoming more common, the
types of light human eyes are encountering is changing, the
researches point out in the journal Eye.
Compared to traditional incandescent bulbs, electronic screens and
low-energy light bulbs tend to emit more blue light, which has long
been known to be toxic to the retina, they write.
Based on that toxicity research, the International Commission on
Non-Ionizing Radiation Protection (ICNIRP) has proposed a safe
exposure limit, below which blue light is unlikely to harm a
O’Hagan and his team measured the blue light emitted by several
sources, including mobile phones, tablet computers, laptops and
lamps, over time periods similar to the way people use the devices.
Then they compared the emissions to the ICNIRP’s exposure limits.
“The aim of our study was to measure blue light from a variety of
sources, see what levels of blue light people were likely to be
exposed to and determine if it was appropriate to issue advice on
the public health aspects,” O’Hagan told Reuters Health by email.
After comparing multiple colors on device screens, the researchers
found that a white screen had the highest blue light emissions, so
they used a white screen set at maximum brightness for their
They also compared the blue light emissions from various devices to
the levels people would encounter when looking at a clear blue sky
in summertime in Chilton, in southern England, and also to an
overcast winter sky in the same location.
The blue light exposure on a clear day in June was around 10 percent
of the ICNIRP safe limit. A cloudy day in December produced around 3
percent of the limit.
Comparing these natural exposures with light from lamps, computer
screens and mobile devices like smartphones, the study team found
that the artificial light produced even lower exposures than people
normally encounter outdoors. That is, provided they’re staring just
at the sky, not directly at the sun, which is well known to damage
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Even considering that people may stare at computer screens for hours
in the course of work or play, the study team concludes that it is
not likely to damage their retinas.
They caution, however, that the amount of light that gets
transmitted from the surface of the eye to the retina is
age-related, so children may be more sensitive to blue light. Light
sources that are comfortable for adults could be distressing for
children, the authors warn.
Meenu Singh, a light spectrum researcher at the National Tsing Hua
University in Hsinchu, Taiwan, told Reuters Health he still has
concerns about the safety of blue light.
“In this time the whole world is going towards digitalization and
people are likely to be spending more time on display devices,"
Singh said by email.
The U.K. study did not look at other questions regarding the effect
of blue light on human health, such as its potential to disrupt
circadian rhythms and sleep.
Singh noted that this is an important consideration. “Displays like
laptops, tablets, and phones should not be used for a long time at
night because its bright emission suppresses the melatonin,” he
To reduce eye strain, Singh said, people should be careful about how
close their eyes are to screens, how long they’re using the device,
and in particular, the brightness of their screens.
“Everyone is different and so individuals are best placed to know
what to do to minimize their own eye strain, including consulting an
optometrist, if necessary,” O’Hagan said.
SOURCE: bit.ly/1TohIJN Eye, online January 15, 2016.
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