emission and transmission of light

Imagine you enter a completely dark room, are you able to see any objects in the room? But when you lit up a candle or torch you can see objects present inside the room, this is because light enables us to see objects. The torch bulb gives out light. The Sun is another source of light. Objects like the Sun that give out or emit light of its own are called luminous objects. What about the objects that we can see like a pencil, table, chair? We see them when light from the luminous objects fall on them and the rays then reach our eyes. They are non-luminous objects.

Luminous Object	Non-Luminous Object
Emit Light of their own. Give us the vision to see the world around us. Example: Sun, Candle, Bulb, torch	Not able to produce light. These Objects are visible due to luminous objects. Example: Books, Table, Chair, Pencils

 

How do we see Luminous objects?

We can see the object when the light is present. Luminous objects produce light that comes directly to our eyes and we can see.

Now the obvious question is -

How do we see Non-Luminous objects?

A luminous object produces light that falls on these non-luminous objects and then light rays from the non-luminous object bounces back or reflected to our eyes and we can see.

Light from the sun falls on the cup and bounce back to your eyes.
Most luminous objects release light together with a large amount of heat.

Question: What is a Moon, a luminous body, or a non-luminous body?
Answer: Moon is a non-luminous body. It reflects the light from the Sun, and that is how we see the Moon.

Transparent, Translucent, and Opaque Object

Objects vary in how they transmit light. Based on how much light an object allows to pass through it, we can categorize the object as transparent, opaque, or translucent. Let us take an example of a wooden fence and try to find the category in which it falls.
 

Transparent	Translucent	Opaque
Materials that allow light to pass through them completely are called Transparent objects.  We can see things lying on the other side of transparent objects.	Materials that allow light to pass through them partially are called Translucent objects. Things on the other side of translucent objects can be seen but not very clear.	Materials that don't allow light to pass through them completely are called Opaque objects. Things lying on the other side of opaque objects cannot be seen at all.
Example: Glass, water, and air.	Example: Oily paper, certain types of designed glass, tissue paper, etc.	Example: wood, metals, etc.

So what kind of object is a wooden fence? Yes, it is opaque.