When the vibrations of electrically charged particles produce energy it is called light energy. Light energy is Electromagnetic radiation. The only form of energy that is visible to the human eye is the light energy. For example: Have you ever noticed the light in the oven used to cook the food? It is a form of light energy.

Light energy is used for various reasons, a few of them are as follows:

• Growth of the human body
• Food formation
• Sight and vision
• Regulation of  physiology
• Drying and evaporation
• Heat and temperature
• For speed regulation
•  Signalling system

A human eye has the ability to distinguish between 6000 different shades of a particular colour and it is possible only because of light. Light has a different electromagnetic spectrum, and each spectrum has seven colours, namely  violet, Indigo, blue, green, yellow, orange, red (VIBGYOR). When light falls on an object, the object absorbs light of some wavelength whereas reflects others. To understand this better, let us now learn what reflection of light is.

The process in which the light rays are sent back after falling on a surface of an object is called reflection of light. The easiest example of reflection would be the image you see of yourself in the mirror or the smooth pool of water. 

Let us now understand the different terms related to reflection:

1. Normal plane: A normal plane is a plane that contains the normal vector of the surface at a particular point.
2. Point of incidence: The point on the surface on which the incident ray strikes the surface is called the point of incidence.
3. Normal: The line perpendicular to the point of incidence at the surface is the normal.
4. Angle of incidence: It is the angle between the normal and the incident ray on a surface.
5. Angle of reflection: It is the angle between the reflected ray and the normal that is drawn at the point of incidence on the reflecting surface.

The law of reflection is defined as “The principal when the light rays fall on the smooth surface,  the angle of reflection is equal to the angle of incidence. Also, the normal to the surface, the incident ray, and the reflected ray, all lie in the same plane.”

The only type of mirror for which a real object always produces an image that is erect, virtual, and of the same size as the object is called the plane mirror.

Virtual and real image:

Virtual Image: An image formed when the outgoing rays from an object move apart (diverge) it is called a virtual image. a virtual image is formed on a plane mirror when positioned behind the mirror.

Real Image: An image formed by the actual intersection of rays of light is called a real image. 

The rays of light actually meet in real image after reflection while in a virtual image it appears to meet but it does not actually meet. We can obtain a real image on the screen but a virtual image cannot be.

Lateral Inversion

The phenomenon in which the left appears to be right and vice versa is called lateral inversion.  This happens due to the direction that light follows when it strikes a reflecting surface, generally on a  mirror. In a plane mirror,  the image is as far behind the mirror as the object is in front of it, and that the front of the image and the front of the object face each other, and hence lateral inversion occurs. For example, the letter “d” when laterally inverted would look like the letter “b” (more or less).

Uses of a plane mirror

• Plane mirrors are used as looking glass.
• Solar cookers.
• In Kaleidoscope.
• In scientific instruments.

Light is a form of energy that plays a vital role in our lives. Light from an object can move through space and it reaches the human eye which enables us to see the things around, be it seeing the screen of the computer or your face in the mirror. We have learnt all the important concepts of light energy.

1. What are the different types of light energy?
   A:  UV light, Visible light, X-rays, Infrared light.
2. Is light energy kinetic energy?
   A: Yes, light energy is kinetic energy. The speed of light is measured to be approximately equal to 3 x 108 m/s.
3. What kind of image does a plane mirror form?
   A:  A plane mirror always forms a virtual image (behind the mirror).
4. What are the characteristics of a plane mirror?
   A:  Characteristics of the plane mirror are as follows:
   a). It always forms a virtual and erect image.
   b). The image size is always equal to the size of the object.
   c). The image that is formed is equally behind the mirror as the object is in front of it.
   d). The images are laterally inverted.
5. What is an example of reflection?
   A: On the surface of a smooth pool of water,  when the incident light is reflected in an orderly manner such that a clear image of the scenery around the pool is seen in it.