1. The Ray Model of Light Light travels in a straight line Recall
Luminous objects produce their own light
A candle is an example of a luminous object that radiates light.
The arrows in this picture represent the paths of light radiating from the candle. As you can see, the candle radiates light in several directions in straight paths which are called Light Rays. A light ray is a line and arrow that represents the straight – line path and direction that light travels in.
Geometric optics uses light rays as an instrument to figure out how light will strike an object.

2. Transparent Objects
Transparent objects allow the incident light to pass through it.
When the incident light strikes a transparent object almost all of the light is transmitted. Therefore, if an object is placed on the opposite side you can see it clearly. As an observer you would be able to see both the shape and color. The small portion of light that is not transmitted would either be absorbed or reflected.

3. Translucent Objects
Translucent objects allow some of the incident light to pass through.
Objects that are translucent can transmit a portion of the light that hits their surface. The rest of this light is reflected or absorbed. As an observer, you cannot see images clearly if they are placed on the other side. You may not be able to detect the objects color, but you would be able to see the shape of the object.

4. Opaque Objects
Opaque objects do not allow any light to pass through it.
All opaque objects reflect or absorb all of the incident light. Therefore no object can be seen through it.

5. What is a mirror?
A mirror is an object that has one polished, reflective surface that is a thin layer of silver or aluminum and an opaque sheet of glass. The opaque portion of a mirror is used to protect the thin layer of silver or aluminum.
When you look into a mirror, you can see an IMAGE. An image is a two-dimensional picture of an object that you can see in a mirror through the use of light. The object can be seen when the light is reflected bouncing back from the mirror to your eyes.
Let’s look at a plane mirror……
A plane mirror has a flat surface and therefore the paths of light are very predictable.

6. Reflection
The incident light refers to the path of light that is emitted from a source and strikes an object. This light ray is called an Incident Ray.
When the Incident Ray strikes the surface of an object, a Reflected Ray will bounce off the object.
We draw a line perpendicular to the objects surface and this line is called Normal
The angle of incidence is the angle between the normal and the incident ray and the angle of reflection is the angle between the reflected ray and the normal.
Normal
Reflected Ray
Incident Ray
Angle of Incidence
Angle of Reflection
Mirror

7. Laws of Reflection There are TWO Laws of Reflection:
1) The angle of incidence equals the angle of reflection
2) The incident ray, the reflected ray, and the normal all lie in the same plane
Light behaves in a very predictable way. The two laws of reflection listed above helps you determine how the incident ray and reflective ray will behave. However, the surface of an object does directly affect how you see a reflected ray.

8. Specular Reflection
When light strikes an object that has a regular surface (smooth, flat, shiny); the reflected light is called Specular Reflection.
Multiple light rays will strike the object and then will be reflected. Each of these light rays will be parallel to each other. (Both Incident Rays and Reflected Rays)

9. Diffuse Reflection
When light strikes an object that has an irregular surface (dull, rough, wavy); the reflected light is called Diffuse Reflection.
Due to the irregular surface, the multiple light rays striking the object will have different angles of incidence and will therefore have different angles of reflection. Each of these light rays will also be scattered and reflected in multiple directions. They do not reflect parallel as you see in specular reflection.

10. In the left hand picture with a rough surface, you can place your eye anywhere and you will see some reflected rays. On the right hand side, you eye has to be in the correct position to see the reflected light. This is called specular reflection.