Electromagnetic Spectrum and Vision
Wave Model of Light
Light Waves
The sun is the most abundant source of direct, natural light on Earth.
There are also forms of energy that are invisible. The tiny band of visible light that we see is only part of the entire spectrum of light energy we receive.
The electromagnetic spectrum is composed of light, electrical, and magnetic waves that vibrate to radiate the earth.
Sources of Light
Natural: Lava, lightning, fireflies, eels, bioluminescence
Man-Made: Light bulb, LEDs, electricity
Radiation
Radiation: Energy traveling through space.
Sunshine is a form of radiation (light, heat, suntans).
We control our exposure through sunglasses, shade, air conditioners, hats, clothes, and sunscreen.
There would be no life on earth without sunlight, but too much of it is not a good thing.
Sunshine consists of radiation in a range of wavelengths from long-wave infra-red to shorter wavelength ultraviolet.
Wave Length Terminology
Light exists on the electromagnetic spectrum, which is composed of radiation waves.
Different wavelengths are seen differently.
Properties of Waves
Amplitude: The height of the wave, measured in meters.
Wavelength: The distance between adjacent crests, measured in meters.
Period: The time it takes for one complete wave to pass a given point, measured in seconds.
Frequency: The number of complete waves that pass a point in one second, measured in hertz.
Electromagnetic Spectrum
The arrangement by wavelength of different forms of EMR (Electromagnetic Radiation).
Includes light, different colors of light represent different frequencies & wavelengths.
The electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.
Application of Electromagnetic Radiation
These waves behave just like visible light (reflected, absorbed, transmitted).
Radio Waves: Radio, MRIs.
Microwaves: Microwaves, RADAR.
Ultraviolet rays: UV light (vit D synthesis).
Gamma Rays: Most powerful/ most energy. Small doses in radiation therapy, bombs.
Applications
Detecting speeding cars.
Sending telephone, satellite, and television communications.
Treating muscle soreness.
Drying and curing plywood.
Curing rubber and resins.
Raising bread and doughnuts.
Cooking potato chips.
Radio Waves
If you could stretch the infrared wave out, it would go into radio waves.
Radio waves have a longer wavelength and a lower frequency than visible light.
Different types of radio waves have different uses.
They are reflected by metal and pass through glass, paper, plastic, and similar material, and are absorbed by water.
Infrared
Infrared radiation is emitted by anything warmer than its surroundings.
Heat energy you lose is actually photons of infrared light, your heat is light.
Practical applications include motion sensors, burglar alarms, and heat lamps.
Visible Light Waves
From the electromagnetic spectrum only wavelengths between micrometers (Purple) and micrometers (Red).
Ultra Violet Light
Ultraviolet radiation is beyond the wavelength of violet light (invisible sunlight), approximately .
Causes tanning but can also do irreparable damage to us.
Ozone Layer
The ozone layer is a form of oxygen surrounding the earth about above ground.
It filters sunlight by absorbing ultraviolet radiation.
X-Rays
X-rays have a very short wavelength that can penetrate skin and muscle but is absorbed by bone.
This radiation always stays in the bone and builds up over time.
Bones and teeth are dense and absorb more X-rays, leaving silhouettes on the X-ray film.
Metal absorbs even more X-rays.
Gamma Rays
Gamma rays are the deadliest and the shortest wavelength & highest (frequency) energy EMR.
Most energetic form of light.
Result from nuclear reactions and can kill cells.
Supernova explosions are sources of gamma-rays.
Radiation therapy uses gamma rays to destroy cancer cells.
Artificial Sources of Light
Incandescent and Fluorescent Light
Energy Efficient Light Bulbs
Natural Sources of Light
Adding Colours together
Television
Types of Light
Natural light sources: Bioluminescence/Photophore
Artificial light sources: Incandescent light, Fluorescent light, Phosphorescent light, Energy-efficient light bulbs
Natural Light - Bioluminescence
The production and emission of light by a living organism as the result of a chemical reaction during which chemical energy is converted to light energy.
Chemical reaction produced by photophores
Artificial Light
Incandescent: Filament, where electrical energy flows through and heating it to extremely high temperatures.
Fluorescent: Glass tube filled with mercury vapor gas and coated with a white powder (phosphor). Electricity passes many times/sec emitting UV. When the UV hits the phosphor produces the light.
Phosphorescent: UV light hits phosphor and stores up energy, emits light after UV light has stopped, glows in the dark, usually in novelty items.
Adding Colors Together
Visible light has a spectrum of colors, each having a slightly different wavelength, each color refracts by a slightly different amount.
All combined together form white light.
All you really need to produce white light are three colors: Red, green, blue (known as the primary colors).
By mixing the right intensities of each color you get white light (Additive color mixing).
Secondary Colours
Colours made by combining any two of the primary colours of light.
How TVs work Mixture of RYB primary colors.
Image Formation in Eyes and Cameras
How Light gets in
Focusing the Light
Image Formation
Correcting Vision Problems with Lenses
Laser Eye Surgery
Night Vision Goggles
The Human Eye and Camera
Both eyes (natural) and cameras (artificial) are image-producing technologies.
A camera is very similar to how an eye works.
Similarities Between an Eye and a Camera:
Feature | Human Eye | Camera |
|---|---|---|
How does light enter? | Pupil | Aperture |
What controls the light? | Iris | Diaphragm |
What interprets the image? | Retina | Film |
How is the light focused? | Lens | Lens |
How Light Gets In
Eye:
Iris: Uses a circular band of muscles to control the amount of light entering.
Iris reflex: Natural changing in the size of the pupils by constricting and dilating.
Pupil: The hole light enters.
Camera:
Aperture: The hole light enters in a camera
Diaphragm: Regulates the amount of light that enters
When Light Gets Inside Eyes
Photoreceptor cells in the retina detect light.
Produce small electrical impulses from the retina to the brain through the optic nerve.
Layers of tissue hold the different parts of the eye together.
The eyeball contains fluids that prevent the eyeball from collapsing and refract the light that enters the eye.
Lens cannot move, so it uses muscles in the iris to change the shape of the lens to accommodate focus.
When Light Gets Inside Cameras
The film at the back of the camera contains light-sensitive chemicals.
These change when light hits it and store the image.
The parts of a camera are inside a hard, light-proof box
Digital cameras use sensors to create an image
The lens focuses the light by moving closer or further away
Image Formation for Eyes and Cameras
Eye:
The eye is a convex lens.
The upside-down image produced by the lens is not a problem because the brain interprets the world right side up.
Camera:
Film is stored in the same orientation.
Can be developed to be flipped or upside down.
Near Sightedness
Can see near but cannot see far.
The eye cannot make the lens thin enough to focus light on the retina, so a concave lens is used to diverge the light onto the retina.
Far Sightedness
Can see far but cannot see near.
The eye cannot make the lens fat enough to focus light on the retina, so a convex lens is used to converge the light onto the lens.
Eye Diseases
Eye diseases that cause pressure and can cause vision loss and blindness by damaging the optic nerve.
Symptoms: eye pain, pressure, headaches, blurred vision
There is no cure for glaucoma.
Cataract & Cataract Surgery
Cloudiness of the lens.
Develops when aging or damage to the eye.
Astigmatism
Happens when your cornea or lens has a different shape.
May be present from birth, or it may develop after an eye injury, disease, or surgery.
Corrected with glasses or contacts.
Laser Eye Surgery
The surgeon cuts a thin flap of tissue covering the eye, folds it over, then the cornea is reshaped with a laser.
The reshaped cornea acts like a corrective lens, allowing the light to be bent so it will properly focus on the retina.
Night Vision Goggles
Light is focused onto an image intensifier.
Inside the intensifier, the light energy releases a stream of particles, which hit a phosphor-coated screen.
These glow green, and the person looking in the goggles can view a green image.
Other Eyes in the Animal Kingdom
Camera Eyes
Compound Eyes
Photoreceptors
Two types:
Rods: Highly sensitive to light to small amounts of light. Allows for seeing in the dark. More rods on the outside of the retina.
Cones: Detect color. Only in the retina.
Photoreceptors Additional Information
Rods can function in low light, cones cannot (only shades of grey appear in low light).
Photoreceptors send messages to the optic nerve, which passages messages to the brain.
The brain sends and receives signals as electrical impulses traveling across neurons, but scientists still don’t understand how the images are stored.
Camera Eyes
Have a cornea, a lens, and a retina.
Vertebrates (animals with backbones) usually have camera eyes.
Camera Eyes Examples
Fish Eyes: Camera eyes with a perfectly round lens, eyes bulge out from the pupil. They do not have necks so need this to see from any angle.
Birds have 5 types of cones instead of 3 like humans' eyes, each sensitive to different wavelengths of light. So, they can see farther.
Octopus eyes, an invertebrate with camera eyes, but the lens is moved instead of a shaped.
Nocturnal Animal Eyes
Nocturnal animals collect as much light as possible because of their very large pupils.
Have many more rods than cones.
They also have a layer called the tapetum which reflects the low light to the retina. Eyes shine at night (Layer inside their eyes acts as a mirror).
Compound Eyes
Insects and crustaceans have compound eyes.
Made up of many smaller unit eyes called ommatidium.
Looks like a long tube with a lens on the outer surface, a focusing cone below it and then a light-sensitive cell below that.
Forms a mosaic image.
Image Storage and Transmission
Stadium Images
Digital Images
Colouring a Digital Image
Digital Image Quality
Capturing Digital Images
Transmitting Digital Images
Stadium Images
The process of creating a big picture out of small pieces, like ones created in a stadium (analogous to digital images).
Digital Images
When a computer receives an image, it divides the picture up into small elements called pixels (picture elements), like the individual seats in a stadium.
Each pixel is assigned a place and is represented by a number.
Transmitting Digital Images
Storing images digitally means that the image can maintain its original quality forever. They won’t fade or get torn as photographs may do.
The computer breaks the image up into squares called pixels and assigns each pixel a co-ordinate. This tells the computer where each pixel goes. It also assigns a value, which tells the computer what colour or shade of grey to make each pixel.
Digital images can be sent over vast distances without having to be processed. A powerful computer can convert the digital information very quickly. Digital imaging can also collect different parts of the electromagnetic spectrum, allowing infrared as well as visible images to be captured.
Coloring a Digital Image
To color a digital image, the computer assigns a value to each pixel which corresponds to a certain color.
Digital Image Quality
The quality of a digital image depends on the size of the pixels.
Large Pixel (less) = Poor Image Quality
Small Pixel (more) = High Image Quality
Resolution
The quality of the image is represented by its resolution.
The more pixels there are in the image, the higher the resolution.
Capturing Digital Images
Scanners, digital video recorders, and digital cameras use a charge-coupled device (CCD) to capture the light.
CCD is a grid similar to graph paper.
As the light enters each grid square it creates a small electrical charge, which is then converted into digital information and stored on a hard drive, compact disk, or digital tape.