Model of Light as Images
Bob Miller, an
artist who worked at the Exploratorium and created many of our
exhibits on light and perception, has developed an elegant way
of looking at light and images. Most of his ideas and explanations
are well described on the Image
Walk web site.
most of his ideas working with the sun as his "light source." Here
we describe an indoor demonstration using an incandescent bulb
as a light source. We recommend that you do this demonstration
only after people have had a chance to extensively experience and
experiment with pinhole images.
- clear light
bulbs with a C-shaped filament
- clamp light
with reflector or a small Square Light Source on its side
- aluminum foil-enough
to cover the reflector or box opening
- screen or
piece of white paper at least 36" x 36"
To Do and
Start with a
clear glass light bulb in a clamp light. The bulb should have a
clearly distinguishable C-shape filament. Clamp the lamp to the
back of a chair, turn off the room lights and shine the light onto
a white screen 8 to 12 feet away.
Ask your teachers
to look at the screen. What do they see? At first glance it may
seem like plain, uninteresting, white light. But Bob Miller sees
it as something very different.
Suggest to the
teachers that perhaps the light is too bright. Cover the light
reflector opening with aluminum foil. Then use a pin to poke a
little hole in the center of the foil. A large, C-shape spot of
light will appear on the screen. Even though your teachers have
experimented with pinhole images, many may be surprised at what
they see. Usually someone will realize that they are seeing an
image of the filament.
When the group
is in agreement that what they are looking at is an image of the
filament, poke a second hole to get another image on the screen,
then slowly poke more and more holes. Soon some of the images will
begin to overlap. Where the images overlap, you will notice that
the light is brighter. That's because the light from two images
are adding together. Allow the teachers to observe and remark on
that phenomenon. That's because the light from two images are adding
together. Allow the teachers to observe and remark on that phenomenon.
Continue to poke
holes. As the design forming on the screen gets messier and messier,
you'll get multiple overlaps. In some areas it will become impossible
to distinguish individual images as the multiple overlapping images
there is more light than darkness on the screen, use the pin to
just rip away the remaining foil. On the screen you will again
see an expanse of diffuse white light. But you won't think of it
as just plain white light anymore. What you have is a confusion
of filament images.
is not plain light, it is information in the form of images. We
normally can't see those images because there is too much information,
too many images tangled and overlapping, creating a grand confusion.
What the pinhole does for us is isolate a single image by blocking
out other images.
This model of
light being composed of a multitude of images is a powerful means
of thinking about the world.
we can be apply this model to outdoor sunlight. When we go outdoors
on a sunny day we see bright, uniform sunlight on the ground. But
under a tree, we may see round patches of light. The tree leaves
block out most of the sun images. But the spaces between the leaves
can isolate single images of the sun and allow them to pass through,
creating a sun image on the ground. We can then understand that
the diffuse sunlight which we initially saw is actually made up
of many overlapping sun images.