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Eye injury caused by the Sun's radiation
Intensive ultra-violet radiation (290nm - 380nm), visible light (380nm -
780nm) and infrared radiation (780nm - 1400nm) can be damaging to our
eyes. Ultra-violet light is known to contribute to the accelerated aging
of the outer layers of the eye and the development of cataract. While
intense visible light damages the eyes' photosensitive cells, thereby
impairing their photo-sensory functions, infrared radiation literally
cooks the sensitive tissues in the eyeball, and can precipitate the
formation of small blind areas in the retina in extreme cases.
Though the sun may look dim, especially through filters, indicating that
most of the visible light is blocked out, the invisible ultra-violet and
infrared radiation can still reach our eyes unabated. As pain receptors
are absent in our retinas, we may not feel immediate pain while our eyes
are being injured. Worse still, symptoms of visual impairment will begin
to appear hours after irreparable damage has already been done.
A solar filter can be regarded as "safe" if it is able to filter
at least 99.9997% of visible light and most of the infrared and
ultra-violet radiation.
Precautions
1.
Do not look at the Sun directly;
2. Do
not look at the Sun through smoked glass, exposed films, ink or
sunglasses; and
3.
Do not look at the Sun continuously for over a minute. Let the eyes have
enough rest from time to time.
Possible ways of observing the Sun
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1. Join
the Solar Eclipse Observation Activities organized by the Hong Kong Space
Museum or local astronomical organizations;
2. Use
a telescope equipped with safe light filtering system. The observation
should be carried out under the supervision of persons with proper
training and expertise. Of the two kinds of filtering systems, external
systems (filtering the Sun's rays before they enter the telescope) is
safer than internal systems (filtering the Sun's rays after they enter the
telescope). Projection method is by far the safest way to observe the Sun;
3.
Observe the Sun with
a
pin hole camera ;
and
4. Use plastic plates
specially made for observing Solar Eclipses.
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Use plastic plates specially made for observing Solar Eclipses. |
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