Light and Vision
How do we see?
The Electromagnetic Spectrum
Things to
Think About Today
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Light waves travel in straight lines until they meet matter
Then, light is reflected, absorbed, refracted
Why do animals have eyes? How did eyes evolve?
What are the parts of the eye and how do they work to
bend light
Light Energy Meets Matter
Refracted (Bent)
Reflected
Absorbed
• Light waves travel in
straight lines until they
meet matter
• Some matter ( lenses)
focus rays and bend them
in defined ways
• Pin activity=Boxes
with solutions/laser
pointer, ray box
• Ray boxes with lenses,
gelatin lenses
Convex Lenses
Magnifying Lenses are Convex lenses
Concave Lenses
(divergent lenses)
Eyes: Detect and Focus Light
• Eyes are organs that detect light, and convert it to
electro-chemical impulses in neurons
• In higher organisms the eye is a complex optical
system which:
– collects light from the surrounding environment
– regulates its intensity through a diaphragm
– focuses it through an adjustable assembly of lenses to form
an image
– converts the image into a set of electrical signals
– transmits these signals to the brain, through complex neural
pathways that connect the eye, via the optic nerve, to the
visual cortex and other areas of the brain.
3 types of eyes have evolved
• Single centered lens
– Advanced mollusks (octopus),
spiders,vertebrates
• Many tiny lenses
– Arthropods (trilobites)
– Ex. Ants (50 images) Horsefly
(7,000 images) Dragonfly
(30,000 images)
• Hole without lens
– snakes
Parts of the Eye that you can See!
Functions of Parts of the Eye
• Eyelid- protection of eye
from injury
• Pupil- hole in the center
of the iris that lets light in
– Appears black because the
eye tissue absorbs most of
the light
• Sclera-tough outer layer
– collagen and elastin
• Iris-colored area
surrounding pupil
– Composed of smooth
muscle
Interior Parts of the Eye
Path of an Image
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Goes through the Cornea and Lens
Hits the back of the retina
Activates rod and cone cells
Transmit impulse through optic nerve to the brain
Rod and Cone Cells
• Rod Cells- numerous ( 130 million in each eye
– Responsible for Twilight vision, Gray shades
– Very sensitive to light
– Found on outside of
retina
• Cone Cells– less numerous
• ( 7 million)
– Responsible for
– Ability to see Color
– Found in center of the retina
• (macula)
Now, let’s think about what
might go wrong
Myopia- Near-sighted
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Genetic Basis
Eye is longer than normal, Cornea steeper
Correct with glasses, contacts, surgery
Very common!
Can make it better by squinting!- Changes
the eyeball shape!
Myopia= Near Sightedness
Hyperopia- Far-sighted
• Image is focused behind the eyeball
• Cornea is flatter, eye is shorter, focusing power is
weaker
• Young people can “accommodate” by changing
shape of eye= As people get older, lens get harder
and can’t be bent.
• Lasix surgery changes shape of cornea
– http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0004853/
Hyperopia+ Farsightedness
Cataracts
• Clouding of the lens
• Caused by aging or damage to the proteins
that make up the lens
• Chemicals, Diabetes, Injury, Smoking are
causative
• Surgery to remove lens
Normal/Cataract
Retinitis Pigmentosa
• Rare genetic disease (1/4000 people in US)
• Rods die and leave dark deposits in retina
• Lose peripheral
and night vision
Normal/Retinitis
What about compound vision?
A Grid- Seen by a
Human and an
Insect
A spider web- seen
by a human and an
insect
Bee as seen by a
mammal and an
insect
Insect images
Insects See Colors Differently
http://www.naturfotograf.com/UV_flowers_list.html
What about other animals?
Bird Vision
• How do nocturnal birds see?
– Rod cells are very sensitive in low light
• Humans have around 200,000/mm2, some owls have over a
million/mm2
– Birds also have larger pupils which let more light in
• What about day foragers
– Have more cones than humans
– May have more than one fovea area of sharpness)
Ruminant Pupils
• Slit-like in bright light,
circular in dim light
• Gives permanent wideangle vision whether in
dim or bright light -makes
watching for predators
more efficient.
Making the connection between
physical science and biology
• Light travels in straight
lines
• Light bends when it meets
matter
• Lenses are matter that bend
light
• How animals see
• Eye diseases
• Do you need light to see?
• Ray box
• Bending Experiment
• Play with Lenses
• Eye Dissection
• Annenberg video
Video
by Discipline
by Grade
Teacher Resources/Education
St udent s t ry t o explain
where wood really comes
from.
A video document ary on educat ion and learning for K-12
educat ors and parent s; 3 one-hour video programs and guide
N o w o n DVD
Why don't even t he bright est st udent s t ruly grasp simple
science concept s? These video programs pick up on t he
quest ions asked in t he Privat e Universe document ary and
furt her explore how children learn. Based on recent research,
as well as t he pioneering work of Piaget and ot hers, M i n d s
o f O u r O w n shows t hat many of t he t hings we assume
about how children learn are simply not t rue. For educat ors
and parent s, t hese programs bring new insight t o debat es
about educat ion reform.
Produced by the Harvard-Smithsonian Center for
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I S B N : 1-57680-064-4
Overview
Individual Program Descriptions
Printable Page
Buy Videos and Materials
RReel a tt e d Re ssoouu r c e ss
See all
A Private Universe
Private Universe Project in Science
Private Universe Project in Mathematics
Surprises in Mind
A Private Universe Project
Wrap up Questions
• What is seeing?
• Can a human being see in the dark? Why?
• How would a scientist test if you could see in
the dark?
Reading Resources
• A Natural History of the Senses-Diane Ackerman
• Video- Annenberg Foundation
• GEMShttp://lawrencehallofscience.org/gems/gemsguides
topic.html
Exploring Light and Lenses
• Concave Lenses and light
• Pinhole Viewer (Camera)
• Camera Obscura
Camera Obscura (CA)
Camera Box