Cannot See
Javier Hernández-Andrés, José
García and Juan L. Nieves Credit
A.
A boy experiences
defective color
vision by using
special glasses.
OPTICS | EDUCATION
Exploring
What the Eye
At Spain’s Science Museum
of Granada, visitors can
explore the limits of human
vision—and how optics can
overcome them.
The human visual system is a masterpiece of optical engineering. It allows
us to navigate the world through depth
perception, peripheral vision and accommodation to different focus distances.
Perhaps just as interesting as what the
eye can do, however, is what it can’t—
including visualizing microscopic objects
or seeing infrared light. Fortunately, for
nearly every visual constraint we have, an
optical technology has been developed to
help compensate for it. Thus, probing the
limits of human vision presents an excellent opportunity to educate people about
optics and the critical enabling role it
plays in our lives.
So, when the Science Museum of
Granada asked us, as members of the
optics department at the University of
Granada, to organize an exhibit that
would engage public interest in science,
we created an interactive exploration
of “what the eye cannot see.” Since our
department specializes in vision and
color vision, we felt well equipped to
bring this exhibit to life.
Each of the following sections
describe a limitation to the human
visual system and some of the demonstrations we devised to illustrate it and
highlight relevant optical technologies.
For each limitation, a scientist-trainer
gave an introductory explanation and
then showed a demonstration in small
groups. Individuals were also invited
to actively participate in some of the
experiments. Many of these ideas and
experiments could be easily replicated in
a classroom setting.
absorb light and then re-emit it under
less-energetic wavelengths and thus glow
under exposure to ultraviolet light. Visitors were given the opportunity to see
in the infrared range by using a thermo-graphic camera that displays images on
a large screen.
For nearly every visual
constraint we have, an
optical technology has
been developed to help
compensate for it.
Spectral limits
The exhibit introduced visitors to the
light that lies beyond the spectral range
that our visual system can perceive—in
other words, ultraviolet and infrared
radiation. A scientist explained how
fluorescent and phosphorescent objects
Intensity of radiation
The human visual system is also limited
with respect to the intensity of radiation it can handle. Human vision is very
restricted in dim light, and, alternatively,
if the eye receives radiation above a
certain limit, it will be blinded and the
retina may be irreparably damaged. The
iris is the first protective barrier for high-intensity radiation, but its effectiveness is
restricted because the minimum diameter is only about 2 mm. Often people
need to use sunglasses as an auxiliary
means of protection.
The exhibit included several experiments related to this topic. For example,
people could see an image intensifier
(night binoculars) in operation; they
could perform the “giant iris experiment,” in which they look at their own
