The human eye
The Human eye is a very intricate device. But, the eye
is useless without light. Nothing can be seen in pitch darkness.
The work of the eye begins only when there is light. How
does the eye work?
The light from the object being seen falls on a special
surface inside the eye called the retina. The retina converts
light to electricity. These tiny bits of electricity (signals)
are carried to the brain by the optic nerve. The brain analyses
these signals and identifies the object. The information
gathered about the object includes its colour; texture (to
some extent); depth (three dimensional aspect); distance
from us and motion.
The amount of light that falls on the retina is very important.
Very strong light can damage it. A mechanism to control
the amount of light is necessary. The iris provides this
mechanism. The iris is the coloured disk of the eye, which
has an opening at the centre known as the pupil. The pupil
is narrow in bright light, thereby allowing only a little
light to enter in and wide in dim light to allow more light
to enter in.