Incandescence: light given off by an object because it is very hot

Luminescence: Light given off by an object that has not been heated

Examples:

Chemiluminescence: light released during a chemical reaction

Bioluminescence: light released by natural sources

Electric discharge: high energy electrons reacting with gases sealed in a glass tube

Flourescene: type of electric discharge where the gases emit UV light which transfers energy to phosphors that release the enrgy as light

Seeing Things

Understanding Sight Requires

• Understanding Light• Understanding the Eye-Brain

http://www.michaelbach.de/ot/mot_adaptSpiral/index.html

The Eye & Brain(- are part of how we see.)

Meet our “Eye-Brain”. We will use these often as observers on diagrams in this unit.

The tip of the candle flame emits light in all directions.

But we only see the light that enters our Eye-Brain.

We don’t see light that does not enter our eyes.

We don’t see light directed away from our eyes unless it is reflected into our Eye-Brain by something.

On diagrams in this unit, we will tend to ignore all light that does not enter our Eye-Brains.

The path light takes is called a Ray.

Diagrams that show how light moves from the object to the eye are called Ray Diagrams.

Light is a type of energy our eyes are sensitive to.

This only tells us how we detect light but it does not tell us what light is.

Can he see the Eye-Brain’s feet?

Light travels in straight lines. This is called Rectilinear Propagation.

Since no ray of light can go straight from the Eye-Brain’s feet into your eyes, you can’t see them.

Experience has trained our Eye-Brain to expect that things are located in the direction that the light comes from.

Newton was the first to note that white light breaks into the colours of a rainbow when it passes through a prism.

These colours are called a Spectrum.

When light from the Sun (White Light) is broken down, it’s Spectrum looks like this.

White Light is made up of shades of Red, Orange, Yellow, Green, Blue, and Violet. A mnemonic for remembering the order of rainbow colours is the name Roy G Biv.

Newton noted that the individual coloured lines could not be separated further.

These lines are pure colours and are identified by a frequency and wavelength number.

The atoms in sources that produce light are surrounded by electrons that can be excited to higher energy levels.

As these electrons fall back to their original energy level, they give off the energy in the form of light.

i.e., incandescence

There are many different ways for electrons to fall back.

Each jump backdown produces a different coloured line of light.

The Conceptual definition of light is; Light is produced when electrons change energy levels.

Our ears cannot hear some high sound frequencies that dogs can.

Similarly, our eyes cannot “see” some of the colours of light.

For instance, you cannot see if an iron is hot or not. Our eyes are not sensitive to the “colour” the iron emits but our hands can feel it.

The “colour” hot irons emit is called Infra Red Radiation.

Some snakes can see Infra Red Radiation.

Similarly, you cannot see water heating in a microwave oven. Our eyes are not sensitive to the “colour” the water can absorb.

The “colour” that water is heated by is called Microwave Radiation.

The Visible Light Spectrum is a very small part of a much larger spectrum called the Electromagnetic Spectrum.

Radio Waves

Microwaves Infra Red Visible Spectrum

Ultra Violet

X-Rays Gamma Rays

Raul's Mother Is Visiting Uncle Xavier's Garden

Rabbits Mate In Very Unusual eXpensive Gardens

Raging Martians Invade Roy G. Biv. Using X-rays & Gamma Rays

Mnemonics for Remembering

the Electromagnetic Spectrum

from Long to Short Wavelength

How is a wavelength defined?

A wavelength is the distance between peaks on a wave.

Draw and label wavelength

Reflection is the process in which light “bounces off” the surface of an object and travels in another direction.

On a ray diagram, the Object’s Location or Distance from the Eye-Brain is where all light rays appear to originate or come from.

To make the ray diagram simpler, we often only use one ray entering the eye. In this case, the Object’s Location or Distance from the Eye-Brain is where all rays originate if the eye changes position.

Atoms in Luminous Objects emit light rays in all directions produced from other energy sources.

Atoms in Non-Luminous Objects scatter the light rays from Luminous Objects in all directions.* We only see the rays that reach our Eye-Brain.

Rays of light travel from the object to the observer’s eye through a Medium. A Transparent Medium allows nearly all the rays to pass straight through unaltered. Example: Air

An Opaque Medium absorbs or scatters all the rays. Example: Your Texbook

A Translucent Medium transmits and scatters the rays. The medium indicates whether it is being illuminated but the object cannot be clearly seen. Example: Wax paper

Two eyes in front of a head can determine the object’s location better because the rays entering each eye can be used by the Eye-Brain to triangulate where the object is. This is called Depth Perception.

Try the Pencil Touch Activity

Floating Finger Procedure 2) Hold your left and right

forefingers about 30 cm in front of your eyes. Hold them horizontally about 2-3 cm apart.

3) Focus your eyes at a far point. Do not focus on your fingers.

4) Wiggle the fingers slightly up and down.

5) Try closing one eye at a time.

Floating Finger

Did you see a piece of finger floating in the air?

Explanation:The eyes are focused on a point located far away. The Eye-Brain uses two slightly different sets of rays to triangulate the distance.

But we still see objects that are closer to the eyes.

Left Eye Image

The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, image depth can only be determined by their relative size.

Right Eye Image

The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye, image depth can only be determined by their relative size.

Images from Both Eyes combined in the brain

The image from the left eye and the image in the right eye are combined in our brain. We see the overlap finger. The overlap is seen more clearly because it is seen by both eyes. You cannot see the floating piece of finger with one eye closed. We are not able to see depth well with only one eye. If we use only one eye image depth can only be determined by their relative size.

The effect of two eyes on depth perception of the Eye-Brain is also used in Magic Eye or Random Dot pictures.

The apparent Size of the object depends on the angle between rays coming from the top and bottom of the object. Large objects have a large angle between the rays.

Objects that are farther away have a small angle between rays coming from the top and bottom. This makes them appear small to the Eye-Brain

Objects that are close have a large angle between the rays, and the object appears larger.

If the Eye-Brain is confused about the location of the objects, then the object’s apparent size (dotted shapes) can be confused.

The Eye-Brain may assume both objects are at the same distance. Then the distant object looks small compared to the close object.

Animals with eyes on the side of their heads can only see the object with one eye at a time. They cannot use the triangulation method to determine the object’s location. These animals must use the object’s apparent size to determine its location. Their depth perception will be poor.

The Moon Illusion is an optical illusion in which the Moon appears larger when it is near the horizon than it does when it is higher up in the sky.

One of the possible explanations of the Moon Illusion is that the eye is confused about the location of the moon and surrounding objects. Therefore, the apparent size is confused.