As per law of energy conservation, Energy can not be created nor be destroyed. Please tell me the answer, suppose i am in a room having glass (mirror) all sides and i lit up the tube. this light reflects and reflect. but if i switch off the lamp. where the light goes? why this light is not been present after switch off the lamp? what distance the light can travel? about the flow of light energy through any medium

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    $\begingroup$ You missed. Physics.SE is thataway. $\endgroup$ Dec 1, 2016 at 8:55
  • $\begingroup$ We appreciate that you think you'll get a good answer on this forum about Electrical engineering even though your questions is very much on Physics for which there is a separate forum. $\endgroup$
    – FakeMoustache
    Dec 1, 2016 at 9:40
  • $\begingroup$ ok sir thanks for your suggestion. can you please tell name of forum on which i can ask questions on physics? $\endgroup$
    – Satish Patil
    Dec 1, 2016 at 10:17

1 Answer 1


A mirror reflects about 90% of the light and wastes about 10% in heat. Light bouncing back and forth 100 times will pretty much be down to zero because $0.9^{100}$ = 0.003%.

Light travels quickly (3 x 10^8 m/s) so in a room that has a return journey of 10 metres, it takes 33 nano seconds for one reflection to return and if this repeated 100 times (as per above) you would see nothing after about 3.3 micro seconds.

How fast does the eye respond - it will look like an instantaneous event.

what distance the light can travel

Well, telescopes can see visible objects that are billions of light years away so you do the math.

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    $\begingroup$ OK, who's the moron pressing the down vote button? $\endgroup$
    – Andy aka
    Dec 1, 2016 at 9:07
  • $\begingroup$ Probably a moron who does not understand physics. +1 because I see nothing wrong with this answer. $\endgroup$
    – FakeMoustache
    Dec 1, 2016 at 9:36
  • $\begingroup$ Have another +1. And one for the OP, because he is thinking! $\endgroup$
    – Neil_UK
    Dec 1, 2016 at 9:43

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