Transcript WhatIsLight?

Unit #3
Light
and
Optical Systems
Topic #1 – What is Light?
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Light is the form of energy you can see!
The Sun is a natural light source
(another natural source is fire)
The Sun is a star and all stars in the
universe are sources of light
Light radiates from stars (in all directions
like spokes on a bicycle wheel)
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Energy such as light that travels by
radiation is called radiant energy
Because the Sun’s energy is not always
available, humans developed light
producing technologies
These sources of light are called artificial
light sources (such as a light bulb)
Because light is a form of energy, when it
is absorbed by a surface it can be
transformed into several different forms of
energy
Ex.
 Light on a dark sweater producing thermal
energy
 Solar cells transforming light into
electricity
 Trees absorbing light to produce sugars –
chemical energy
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Sources of Light
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What if there was no natural sources of
light?
Early civilization used torches, lanterns,
candles
Now we have light from lamps,
computers, televisions and other newfangled gadgets
Here are some sources of light….
Incandescent Sources
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An object can be heated to such a high
temperature that it emits visible light
Such an object is called an incandescent
source of light
The emission of visible light by a hot
object is called incandescence
Example: filament light bulbs
Tidbit – almost 95% of the energy given
off by an incandescent light bulb is
released as heat!
Fluorescent Sources
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When you stand under a “black light”,
you may notice that your white clothes
glow!
In this process, high energy, ultraviolet
light is absorbed by the particles in the
fabric
The particles in the fabric then emits some
of this energy as light you can see.
This glow is called fluorescence
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A fluorescence light bulb uses this energy
transformation
Electricity is run into the ends of the bulb
which is filled with mercury vapor
The mercury vapor emits ultraviolet
radiation which is absorbed by the
phospor coating on the inside of the bulb.
This causes the coating to glow and
produce visible light
Mercury vapor inside the tube is toxic!
Phosphorescent Sources
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Phosporescent sources of light are similar
to fluorescent sources
Light is absorbed by certain particles that
store the energy and release it later as
visible light
The persistent emission of light following
exposure to and removal of a source of
radiation is called phosphorescence
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The main difference between a fluorescent
source and a phosphorescent source is
that the particles in the fluorescent source
release their light energy immediately
Examples:
Star and moon stickers you can put on
your ceiling
The dials of older watches or clocks
Chemoluminescent Sources
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Light can also result from the energy
released in chemical reactions
The chemical reaction produces energetic
particles that give off visible light energy
This process is chemoluminescence
Examples:
Glow sticks can be broken to mix two
chemicals that react and release light
Bioluminescent Sources
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If you were moving through the darkest
depths of the ocean, you may be surprised
to see glowing creatures
They rely on chemical reactions within
their bodies to provide energy for light
This special type of light produced in living
creature is called bioluminescence
Examples: deep sea fish, plankton,
jellyfish, fireflies
Other Facts
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All objects that emit light are said to be
luminous
So how can you see non-luminous
objects that do not emit light?
We’ll find out later on… enough for today
Or is it………………?