Reflection and Absorption
What does reflection mean?
Reflection means that something is thrown back. If you, for example, throw a ball against a wall and it comes back to you, you could say that it has been reflected. The same happens with sunlight meeting the surface of the earth: It is being reflected and can thus be collected by a satellite.
If the light makes contact with a smooth surface such as a mirror the equation is: angle of incidence = angle of reflection. The angle of incidence is the angle between a light ray meeting a surface and the surface itself while the angle of reflection is the angle between the light ray being reflected and the surface.
The principle of the specular (mirror-like) reflection is illustrated in the animation below. Use the mouse in order to point the laser in a new direction and see how both the angle and the reflection of the laser change.
Click on the laser in order to point it in a new direction and see how both the angle of incidence and the angle of reflection change.
There are generally three types of light reflections. However, please note that the reflection depends upon the surface roughness of an object.
1. Specular (mirror-like) reflection: The light ray meets a smooth surface and the angle of incidence is identical with the angle of reflection.
2. Diffuse reflection: The light ray meets a rough surface and is equally reflected in all directions.
3. Mixed reflection: The light ray meets a very rough surface and is unequally reflected in all directions. This type of reflection is the most common one in nature!
Three types of light reflection: The mixed reflection (right) is the most common one in nature.
What does absorption mean?
Surfaces do not only reflect light; they also absorb it. In doing so, the absorbed light energy is being stored and then gradually emitted in the form of warmth. This kind of energy conversion is called absorption.
The animation below illustrates that different objects absorb in different intensities
Please meet Ben the beach bean. You can change Ben’s colour by clicking on the colour fields on the right-hand side. What do you see? The lighter his colour, the less warm and the happier he is! He reflects more light than he absorbs and thus collects far less warmth than if he was wearing a darker colour!
You can transfer this to your everyday life: For example, a black t-shirt absorbs much more sunlight than a white one. This is why in summer you tend to sweat more if you are wearing a black t-shirt than if you are wearing a white t-shirt.
Click on the colour fields on the right-hand side in order to change the looks of Ben the beach bean. What can be observed?
Electromagnetic waves such as the sunlight can be reflected and absorbed. Reflection means that they are being thrown back by a surface; absorption means that they are being collected by a surface and transformed into thermal energy.