An Introduction to:
Light
Created by Anna Opitz – July 2007
Why is light important?
• Light allows us to see.
• Light carries information from our
surroundings to our eyes and brain.
Image: Eye Chart
• Light enables us to communicate
and have contact with the world
around us.
Image: Times Square, NY
How do we use light in our everyday lives?
Photo: Sunglasses
•
•
•
•
•
Photo: Camera
DVD’s
Telecommunications
Television
Lighting
LCD (Liquid Crystal Display)
Photo: iPhone and iPod
Photo: Microscope
• Astronomy
• Microscopy
• Sunglasses
• Cameras
• Photosynthesis
What is light?
In the early 1900’s, scientists had two different
models for the behavior of light:
1. A model where light acts as a particle
2. A model where light acts as a wave
Particle
Wave
So, which model is correct?
BOTH
Light can behave as a particle and a wave at
the SAME TIME!
Waves
Image: Water Waves
Image: Water Wave
• A wave is something as simple as the
ripples from tossing a rock into water or
doing “the wave” at a football game.
• Energy is transferred in a wave, but the
medium through which the wave travels
does not move.
Light as a Wave
Image: Light Wave
Image: Light Wave
• Light is considered an electromagnetic wave
• Electromagnetic waves
are the result of the
meeting of electric and
magnetic fields
• Light travels at a speed of 299,792,458 m / s
Image: Electromagnetic wave
• IMPORTANT DIFFERENCE: Unlike other
types of waves, electromagnetic waves DO
NOT require a medium to travel through!
Properties of Waves:
• Amplitude: half the height of the
wave
• Frequency: measure of number of waves that pass a
given point in a given amount of time
• Wavelength: distance between
two identical points on the wave
• Speed: how fast the wave
travels, given by the wavelength times the frequency, or
v=λf
Focus On: Wavelength
• When studying waves, the wavelength tells
us a lot of information about the wave.
Remember! The wavelength is
the distance between two identical
points on the wave
The wavelength (λ) of a
wave is given by the formula: λ= v ÷ f
Where: v= velocity of wave
f= frequency of wave
• It is important to study the wavelength of light,
because it tells us about the color of light…
The Color of Light
• Light waves have different wavelengths and these
wavelengths correspond to colors in the visible light
spectrum
• The colors we see are actually light waves at different
wavelengths
• Each color has a specific wavelength at which it is
visible to the human eye
• Red light has the longest wavelength at
about 700 nanometers, while violet light
has the shortest wavelength at about 400
nanometers
• White light is all of the different color
waves seen together
Light as a Particle
Image: Photons
Image: Photon
• Light is made up of particles called photons
• Photons are tiny packets of energy
• The energy of a photon is dependent upon
it’s frequency and is given by:
E=hf
E- Energy
h- Planck’s constant
f- frequency
• Higher frequencies correspond to higher
energy photons and lower frequencies to
lower energy photons
How do we create and control light?
Light bulbs are a source of artificial light
resulting from incandescence (thermal
radiation due to temperature)
Light Emitting Diodes, or LEDs, are tiny light
bulbs that are illuminated by the movement of
electrons in a semi-conductor material
Lasers produce light beams at one specific
wavelength (one color), that are very strong
and concentrated
How do we measure and study light?
Light enters the eyes, where impulses are
transmitted to the brain, and the brain identifies
light
Cameras record the light pattern of real images
on light sensitive material
Spectrometers obtain a spectrum of the colors
that make up a particular light
Light detectors convert light power into electrical
power
Why is it important to study light?
Image: Fiber Optics
Image: DVD
Image: CD
• The study of light is called Optics
• Leads to the development of products
applied in modern technologies, such as;
DVDs, CDs, fiber optics
What are some applications of light?
• Medical: X-rays,
laser eye surgery
• Media: television,
movies, paintings,
CDs
• Industrial: laser
cutting,
photolithography,
communications
• Scientific:
spectroscopy,
forensics,
identification of
elements
Image: X-Ray
Image: Laser cutting
Image: Television
Image: Forensic laser use
What is Spectroscopy?
• Spectroscopy studies the way an object’s light
divides into it’s component colors
The image shown to
the left are the spectra
patterns for H, He, N,
Ne, Ar, and Hg gases
• Through analysis of an object’s light, physical
properties such as; luminosity, mass,
temperature, and composition can be
determined
• Data is obtained using a spectrometer, which
works like a prism
What is the future of light?
Nano-sized Light Sources
Nano-sized light sources would make it possible
to look inside individual cells, bio-image on the
nano scale, advance cyber cryptography, and
study light on the nano scale.
Image: Nano-wire Light
Quantum Computers
Quantum Computers would be able to store more
information and also perform much faster than
the computers we use today.
Image: Quantum Chip