Optical Medium: Any material (or) non-material through which light energy passes wholly (or) partially is called optical mediumĢ. Non-luminous Bodies: The bodies which do not give light energy by themselves, but reflect the light energy falling on them are called non-luminous bodies. Examples: The sun, the stars, glow worm etc. Luminous Bodies: The bodies which give out light energy by themselves are called luminous bodies. It means the speed of light is 300000000 m/s or 300000 km/s. Speed of Light: Light travels at very fast speed i.e., 3 × 10 8 m/s. In addition to it, lighted bulb, a fluorescent tube, a lighted candle ,a kerosene oil lamp, etc., are other sources of light. Sources of Light: Sun is the primary source of light for mankind. Thus, we can conclude that light is an invisible energy which causes in us sensation of vision. It is the brain which finally makes out the colours of the poster.
The various colours reflected from the poster excite the retina of the eye, which in turn sends a message to the brain. It must be kept in mind that light energy makes the surrounding objects visible, but by itself it is an invisible energy.Įxample: If we are seeing a coloured poster, then we are seeing only the poster and not the coloured lights reflected fronts it. Since light is obtained from heat energy, i.e., when an object is heated to a temperature beyond. It shows that for vision the presence of light is essential.ĭefinition of Light: It is an invisible energy which causes in us sensation of sight (vision). However, if a bulb is switched on, everything in the room becomes visible.
If we enter a dark room, objects present there are not visible.