Transcript Underwater Light

Let there be light (and color)!
What is Light?
• Light is a type of Electromagnetic (EM)
Energy.
• Visible light is a small part of the EM
spectrum that we can see.
• We can see a range of wavelengths
spanning from approximately 430nm to
790nm.
Where does light come from?
• It all starts with ATOMS
• A nucleus surrounded by electrons that
orbit.
• Electrons stay in the same orbit unless
energy is added to or taken away from the
atom.
• When energy is added, electrons jump to
higher orbits.
Where does light come from(2)
• When the atom gives up energy, electrons
jump back to original orbits.
• As they jump back, they emit light in the
form of photons.
• The bigger the jump, the more energy the
photon carries.
• The amount of energy the photon carries
determines the color of light produced.
Colour
• White light is not a single colour; it is
made up of a mixture of the seven
colours of the rainbow.
We can demonstrate this by
splitting white light with a
prism:
This is how rainbows are
formed: sunlight is “split up”
by raindrops.
Color of Light (Cont.)
• Color of Objects
– White light is the presence of ALL the
colors of the visible spectrum.
– Black objects absorb ALL the colors and no
light is reflected back.
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Seeing color
• The color an object appears depends on the
colors of light it reflects, all other colors are
absorbed.
For example, a red book only reflects red light:
White
light
Only red light
is reflected
A pair of purple pants would reflect purple light (and red
and blue, as purple is made up of red and blue):
Purple light
A white shirt would reflect all seven colors:
White
light
Using colored light
• If we look at a colored object in colored
light we see something different. For
example, consider a soccer uniform:
Shirt looks red
White
light
Shorts look blue
• In different colors of light this uniform would look
different: The shorts look black because there isn’t
any blue light to reflect.
Red
light
Shirt looks red
Shorts look black
• In different colors of light this uniform would look
different: The shirt looks black because there isn’t
any red light available to reflect.
Blue
Shirt looks black
light
Shorts look blue
What happens to light when it
passes through water?
• When light strikes a surface it can be
affected in a number of ways.
• When light strikes the surface of water
some of it is reflected and some is
refracted.
• Water molecules also tend to scatter blue
light but absorb most other colors.
• Different colors are absorbed at different
depths.
Light penetration in the ocean
• The ocean is broken into zones base on
how deep light can penetrate.
– Euphotic Zone- light intensity allows for
photosynthesis.
– Disphotic Zone- enough light to see but not
enough for photosysthesis.
– Aphotic Zone- not enough light to see.
– Depths of these zones can vary depending on
the clarity of the water and the intensity of the
sunlight.
The waves can pass through the object
The waves can be reflected off the object.
The waves can be scattered off the object.
The waves can be absorbed by the object.
The waves can be refracted through the object.
Underwater Light
• Red, orange and yellow
light is absorbed within a
few meters of the surface.
• Green and purple can
penetrate a little deeper.
• Towards the bottom of the
Photic Zone only blue
light is available.
• Red and orange
animals in deep water
look black.
The pictures below show the same
photograph taken with and without
a flash.
Marine animals use light and color
to communicate.
Marine animals use light and color
to confuse attackers.
• Because it is red the shrimp below looks black
underwater where there is no red light. Only the
blue cloud is visible to the fish.