What is photosensitive epilepsy?
Photosensitive epilepsy affects approximately
one in five-hundred people with epilepsy.
In this condition, all (or almost all) seizures
are triggered by flashing / flickering lights,
or certain shapes / patterns. Photosensitive
epilepsy usually affects people before the
age of 20 ( 7-19 years being the most common
age of onset) and girls are more likely
to be affected than boys.
The lights / patterns that trigger seizures
in people with photosensitive epilepsy can
be natural or artificial. In some cases
seizures can be caused simply by sunlight
being reflected off wet leaves, or streaming
through the leaves of trees.
What frequency of light can trigger
seizures?
Most
people with photosensitive epilepsy are
sensitive to frequencies of light between
16 and 25 Hertz (Hz). However some may be
sensitive to rates as low as 3 Hz or as
high as 60 Hz.
Photosensitive epilepsy and computers
Although some images displayed on a computer
screen may be problematic, computers themselves
are very unlikely to trigger seizures in
people with photosensitive epilepsy. It
is useful, however, to be aware of the following
information:
Cathode tube ray (CRT) monitors
CRTs are traditional, large monitors, and
these have scan frequencies ranging from
60 to 100Hz and above. As most people with
photosensitive epilepsy are sensitive to
16-25Hz, CRTs (provided they are set to
refresh rates greater than 70Hz and are
not faulty) are unlikely to trigger seizures.
Liquid crystal display (LCD) monitors
These are thin, flat, non-flickering screens,
and are unlikely to trigger seizures.
Images on monitors
If the material on a computer contains flashing
/ flickering lights, or repetitive patterns,
they will carry the same seizure risk whether
it is observed on a CRT or LCD monitor.
However, because LCD monitors project a
sharper image, they will carry more seizure
risk than CRT if the person with photosensitive
epilepsy is sensitive to patterns with high
contrast.
Anti-glare screens
Anti-glare screens can be used to reduce
glare from a computer. However, because
they don't affect the flicker rate of the
montitor / image, they are not of particular
benefit to people with photosensitive epilepsy.
Interactive whiteboards
Interactive whiteboards are being used increasingly
in schools, and as they do not flicker,
they are unlikely to trigger seizures. However,
as with computers, if the images shown on
the whiteboard have high contrasting patterns,
or flicker at the 'wrong' frequency, these
will carry their own seizure risks.
Media and entertainment
Flashing lights
often feature in the media and entertainment
industries. Click
here to access the latest Office of
Communications (Ofcom) guidance notes, outlining
the correct broadcasting code regarding
photosensitive epilepsy.
