The Wave Model of Light
Properties of Waves
- Amplitude: the height of the wave, measured in meters.
- Wavelength: the distance between adjacent crests
- Period: the time it takes for one complete wave to pass a given point
- Frequency: the number of complete waves that pass a point in one second
- White light is refracted and splits into the colors of the rainbow
- Produces visible light spectrum
- Colors of visible light: Each color of light is refracted at a different angle
- White light being refracted produces the colors of visible light
Wave Model of Light
- Model used to explain the characteristics and behavior of light energy
- Light is an energy in the form of waves
- Different colors of light have different wavelengths
- Waves with shorter wavelengths have higher energy than those with longer wavelengths
The Electromagnetic Spectrum
- Whole world of energy that we cannot see
- Wavelengths that make up visible light are a small part of electromagnetic radiation
- Human eyes can only see a very small portion of this spectrum (the visible light component)
Applications of electromagnetic radiation
Although we can’t see, these waves behave just like visible light (reflected, absorbed, transmitted):
- Radio Waves
- Radio, MRIs
- Microwaves, RADAR
- Ultraviolet rays
- UV light (vit D synthesis)
- Gamma Rays
Producing Visible Light
2 types of light
Natural light sources:
- Bioluminescence (photophore)
Artificial light sources:
- Incandescent ligh
- Fluorescent light
- Phosphorescent light
- Energy efficient light bulbs
Artificial Light Sources
Filament, where electrical energy flows through and heating it to extremely high temperatures. High temperatures cause light to be emitted.
Glass tube filled with mercury vapour gas and coated with a white powder (phosphor)
- Electricity passes many times/sec emitting UV.
- When the UV hits the phosphor produces the light
- Slightly different from fluorescence
- UV light hits phospor and stores up energy
- Emits light after uv light has stopped and glows in dark
- Usually in novelty items
Which is the best ?
Many factors come into play:
Natural Light Sources
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
The Colours of Light : Adding Colours Together
- Visible light has a spectrum of colours, each having a slight 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 colours:
- Red, green, blue
- By mixing the right intensities of each color you get white light
Colours made by combining any two of the primary colours of light
Image Formation in Eyes and Cameras
How Light Gets In
- Both eyes (natural) and cameras (artificial) are image producing technologies.
- A camera is very similar to how an eye works:
Similarities Eye Camera
How does light enter? Pupil Aperture
What controls the amount of light? Iris Diaphragm
What interprets the image? Retina Film
How is the light focused? Lens Lens
A set of doors that opens when you take a picture, the longer it is open the more light that strikes the film in a camera
- The pupil is the opening; the amount of light that enters is controlled by the iris.
- The iris is made up of a circular band of muscles.
Iris Controlling the Light
- In bright light the iris constricts, becoming smaller, and reduces the light.
- In dim light the iris dilates, becoming larger, and increases the light.
When Light Gets Inside…
To see, the light must hit the sensitive retina at the back of the eye, which has 2 types of light sensitive photoreceptors:
- Highly sensitive to small amounts of light (dim light).
- Allows for seeing in the dark (when there is enough light reflected!!)
- More rods on the outside of the retina
- Sensitive to bright lights, and they detect colour.
- Almost exclusive in the retina
- Cones can’t function in low light, so we only see shades of gray in low light because only rods are stimulated
Focusing the Light
- In order to form a clear & sharp image the focal point must land on the retina.
- In the eye there are muscles that control the shape of the lens.
- In a camera the lens is moved forward and backward.
- The upside-down image produced by the lens is not a problem because the brain interprets the world right side up, and film can be developed either way.
Correcting Vision Problems with Lenses
- Nearsightedness – can see near, but cannot see far.
- The eye cannot make the lens thin enough to focus the light on the retina, so a concave lens is used to diverge the light onto the retina.
- Farsightedness - 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.
Laser Eye Surgery
- the lens is reshaped by a laser (helps focus light).
Night Vision Goggles
- the low light is intensified by phosphor-coated screen (looks green).
Other Eyes in the Animal Kingdom
Similarities between human and animal eyes
- Humans, like most vertebrates have a rounded cornea, lens, and retina, which are referred to as camera eyes.
How do eyes function for different animals?
- Fish - have a perfectly round lens sticking out of the pupil, which allows them to detect danger from all directions since they do not have necks.
- Birds - have 5, instead of, 3 cone receptors (RGB) which helps because they must see from further distances because they fly.
- Nocturnal animals - are usually awake at night, they have many more rods to capture more dim light, and they have very large pupils, to capture more light. They also have a layer called the tapetum lucidum, which reflects the low light to the retina.
- Octopus - an invertebrate with camera eyes, but lens is moved instead of shaped.
- Insects and Crustaceans have compound eyes, which are make up of many individual units called ommatidium
- These eyes are great for detecting movement, but not for creating a single coherent image.
- Do not see color
- Do not see 1 image, but many small images put together
Image Storage and Transmission
- The brain sends and receives signals as electrical impulses traveling across neurons, but scientists still don’t understand how the images are stored.
- If you take any form of information and convert it into numbers, that’s digital.
- The process of creating a big picture out of small pieces
- Like ones created in a stadium is similar to the process of digital imaging.
- Therefore, stadium images are analogous to 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.
Coloring Digital Images
- 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 resolution.
- A picture with lots of small pixels has a better resolution than a picture with a smaller number of large pixels.
Capturing Digital Images
- In a digital camera, the light falls onto a charge-coupled device (CCD), which is a grid similar to a piece of graph paper.
Transmitting Digital Images
- The first major advantage of digital imaging is that it can easily be sent great distances, the second is that it can collect others parts of the electromagnetic spectrum (such as infrared).