1. The classification of a material as transparent, translucent or opaque is determined by how light interacts with the material.

A transparent material transmits most of the light that strikes it. This allows objects to be seen clearly through a transparent material. A translucent material transmits some of the light that strikes it. This allows objects to be seen through the material, but not as clearly as through a transparent material. An opaque material transmits none of the light striking it, making it impossible to view objects through an opaque material. 

2. When light interacts with an object, it may be reflected, transmitted, and/or absorbed.

Light always interacts with an object in more than one of the above ways. Whenever light strikes the surface of an object, some of the light is reflected (or scattered). This is what allows us to see the object. Additionally, all objects absorb some of the light that falls on them. This light that is absorbed is converted to heat.

3. Whenever light is reflected from a surface, the angle each incident light ray makes with the normal to the surface is equal to the angle that the reflected light ray makes with the normal. This is known as the Law of Reflection.

The incident ray, the normal and the reflected ray all lie in the same plane.

There are two types of reflection:
a. diffuse reflection (or scattering)
Whenever a beam of parallel light rays strike a surface that is rough, even at the microscopic level, the light rays reflected from the surface are scattered in many directions. This is called diffuse reflection or scattering.  Even though the reflected light is scattered, the Law of Reflection applies to each individual light ray.

Scattering is the kind of reflection that most typically occurs when light strikes the surface of an object. It allows persons located at different positions around an object to be able to see the object.

b. specular reflection
Whenever a beam of parallel light rays strike a surface that is very smooth, the light rays that are reflected from the surface will also be parallel to one another.  

Specular_reflection 

This kind of reflection is called specular reflection. It is what allows us to see an image in a mirror or other surface that is very smooth and highly reflective. In order to see the image of an object in a mirror or mirror-like surface, your eye must be positioned to receive light rays from the object that are reflected from the surface. The image in a plane mirror is located the same distance behind the mirror as the object is in front of the mirror. This is because the light rays from the object that are reflected from the mirror and into the eyes of an observer APPEAR to have come from a place which is the same distance behind the mirror as the object is in front of the mirror.

 This type of image is called a virtual image.

4. Light may be refracted when it passes from one material to another.

Light travels at different speeds through different materials. Generally, the denser a material, the slower light travels through it.

This causes light to change its direction, or bend, as passes obliquely (at an angle) from one material to another. This bending of light is called refraction. The amount of bending depends on the difference in the speeds at which light travels through each material.

When light passes from a material in which its speed is faster to one in which its speed is slower, it is refracted toward the normal. An example of this is the passage of light from air into water. There would be an even greater bending toward the normal when light passes from air into glass. 

When light passes from a material in which its speed is slower to one in which its speed is faster, it is refracted away from the normal. An example of this is the passage of light from water into air.