The Electromagnetic
Spectrum and Sources
of Light
What is Light?
• Light is a form of energy. It is one of several
forms of energy we receive from the Sun as
part of the solar radiation it produces.
• The energy from the Sun travels to Earth as
electromagnetic waves. These waves can
pass through the vacuum of space or
materials on the Earth’s surface.
• Electromagnetic = it affects both electrical and
magnetic fields!
Energy in Waves
• A wave is a disturbance that transfers
energy from one point to another
without transferring matter.
• Waves can be described using their
physical characteristics and/or
properties.
Properties of Waves
• Crest – the highest point on a wave.
• Trough – the lowest point on a wave.
• Rest Position – the level of a fluid (like
water) when there are no waves
passing through it.
Properties of Waves
The Motion of the Ocean
• Wavelength (λ) – The distance from one
place on a wave and the next similar place
on the wave. (Crest to crest or trough to trough
are most common.)
– Wavelength is measured in metres (m).
• Amplitude – The wave height from the rest
position to the crest, OR, the wave depth
from the rest position to the trough.
– Amplitude shows the energy carried by the wave.
• Frequency (ƒ) – The rate of repetition of a
wave.
– Frequency is measured in Hertz (Hz) which in
cycles per second.
Frequency & Wavelength
• Frequency and wavelength have an
inverse relationship. (As one goes up, the
other goes down.)
• The speed (v) of the wave is
determined by multiplying the
frequency (ƒ) by the wavelength (λ).
v=ƒxλ
PROPERTIES of Waves
https://www.youtube.com/watch?v=01Jcz6t9UQg
The Spectrum of Visible Light
• The light that comes from the Sun or a source
like a candle is called visible light. It is the
light that is visible to the human eye.
• Over 300 years ago, Sir Isaac Newton passed
visible light through a triangular piece of glass
called a prism and separated the light into its
component colours.
• The pattern of the colours makes the name
“ROY G. BIV” and is known as the spectrum of
visible light.
The Visible Light Spectrum
The Electromagnetic Spectrum
• Visible light is just one type of
electromagnetic energy. There are also radio
waves, microwaves, X-rays, and gamma rays.
All of these are found in the solar radiation of
the Sun.
• All of the electromagnetic energy can be
arranged to form the electromagnetic
spectrum. It arranges all of the energy in solar
radiation in order from weakest to strongest.
• Visble light is only a small fraction of the
electromagnetic spectrum.
The Electromagnetic Spectrum
Sources of Light
Categories of Light
• We categorize light based on the
source of the light.
• We say an object is luminous when
it emits or produces light.
• Light may be:
–
–
–
–
–
Incandescent
Fluorescent
LEDs
Chemiluminescent
Bioluminescent
Incandescent Light
• Incandescence is the light
produced when an object is heated
to a really high temperature.
• Older light bulbs have a filament,
that gets very hot as electricity is
passed through it, that gives off the
light.
• These lights are inefficient and not good for the
environment because most of the energy put into
them is lost as heat (rather than light).
How A Light Bulb Works!
http://www.youtube.com/watch?v=YnMP1Uj2nz0
Fluorescent Light
• Fluorescence occurs when a substance
absorbs high energy UV radiation and
immediately releases that energy as
visible light.
• A current is passed through the tube of
the light. It excites the mercury and
argon in side the tube and they give off
UV light.
• This UV light reacts with a chemical
that coats the tube and it glows – the
chemical coating shows fluorescence!!!
How Fluorescent Lights Work!
http://www.youtube.com/watch?v=rS5LC2aH0c4
LEDs
• LED stands for light emitting diode.
• An electric current passes through
an LED and it emits light.
• LEDs are very energy efficient and
are replacing many of the other
forms of light.
• LEDs save energy, last longer and stay cooler.
Chemiluminescence
• Chemiluminescence occurs when
two chemicals react and give off
light energy.
• Light sticks contain two chemicals
that mix when you crack the stick
and shake it to mix the chemicals.
• A dye used inside the tube will determine the
colour of the stick.
• Party-goers, campers and law enforcement all
make use of this chemical light form.
Chemiluminescence
Bioluminescence
• Bioluminescence occurs in a living
organism. Chemicals produced in
the organism are mixed together to
produce the light.
• We see this phenomenon in
fireflies, jellyfish, fungi and
bacteria.
Bioluminescence
Bioluminescence
What about the Moon?
• The moon appears to give off light
but it is actually non-luminous –
meaning it does not produce its
own light.
• The moon only appears to give off
light because it reflects light from
a luminous object – the Sun.
Light Off of the Moon
THE END