Question

When we imagine light as a ray, when a bulb is switched on light ray leaves it. However as we switch off it, there is no light ray is in the room. So does it mean that the bulb takes in all the light?

Answer 1

Not at all . The bulb doesn't take it all.

First , as you say let us assume light as a ray .
Bulb is switched on in a dark room. So, room is now bright.The bulb produces several rays of continuous light, not just one ray. Leave the bulb on for 30 minutes. After 30 minutes does the brightness of room increase?? We have put the light on for half an hour right?? So, at each second , bulb is releasing more and more light. So, light intensity or brightness should have increased. But has it??

Answer is NO. Why??
Because, we consider bulb only. Bulb produce light. It is released to the room. But , the walls of room , the air in room, and all other surfaces , including the bulb cover, etc absorb light. All bodies will absorb energy like heat , light etc , at least in small amounts.

So, the light released by bulb is dissapated (absorbed / lost) or degraded(converted to other forms like heat ) as it is absorbed by surfaces. The surfaces gain energy, in some cases , light energy is converted to heat , and so on.

So , to keep the room brigt , either you need to remove all surfaces(it is not possible) or keep light on .

So, when you switch off the bulb, the light released by bulb is completely absorbed or dissapated, and no new light rays are given, so the room becomes dark again. The complete energy, is not absorbed by bulb alone. All surfaces absorb it. It includes the bulb also.