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Trapping light without electricity

  1. May 16, 2014 #1
    Hello all,
    I would like to know a method to trap light. That is, it should be pretty simple and non-electric. It doesn't need to trap all light, just part of it at the least. It should also be able to give out light by itself if certain conditions are met (which conditions do not really matter as long as it is possible for the average person). It also cannot be a fluorescent or luminescent material and the likes. My idea was to create a box that has partial mirrors, like those windows where depending on which side you are, you see your reflection or you see through depending on the brightness inside and outside the box.
    Any other ideas would be appreciated.
    Thanks
     
  2. jcsd
  3. May 16, 2014 #2

    UltrafastPED

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  4. May 16, 2014 #3

    jbriggs444

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    Plant a tree. Expose it to sunlight. Chop it down. Build a campfire.
     
  5. May 16, 2014 #4

    Simon Bridge

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    I'm with jbriggs444, but I suspect that would be ruled out for the same, unspoken, reasons as flourescent or luminescent materials ... phosphorescence is probably ruled out as well, as with any method of storing light in some from other than as, well, light.

    The link in post #2 discusses total internal reflection optical fiber, but the objections work for the mirror-box as well. reminds me of the Wise Men of Gotham story with the windowless church.
     
  6. May 16, 2014 #5
    Thanks for the discussion. It was quite helpful but didn't really answer all my queries. Actually this would have helped me for my science project. This consisted of improving the bottle lightbulb invented by Moser. It was an interesting invention but would work only during the day. It consisted of a plastic bottle filled with water that would refract sunlight and light up. However since it couldn't strs sunlight, it would only light up during the day. The aim was to make it light up at night. As mentioned before, my idea was a partial mirror box. That would trap light during the day as it would allow light in but not out due to being only partially reflective. If anybody has anymore ideas, I would appreciate it. Or if there is any flaw in this idea, point it out. Thanks.
     
  7. May 16, 2014 #6

    adjacent

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    Why do you think it would work? We don't have perfect mirrors. Light will eventually be absorbed by the glass and will be lost.

    This discussion may help:https://www.physicsforums.com/showthread.php?t=721907
     
  8. May 16, 2014 #7
    It was not supposed to infinitely trap the light. Therefore I thought that since a night is shorter than a day(by about 4-5 hours here) if it received enough light during the day, it would give out whatever remained at night, when the amount of light would change.
     
  9. May 16, 2014 #8

    Simon Bridge

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    1. nighttime is only shorter than the daytime in summer.

    2. don't let the word "eventually" mislead you - light goes very fast so "a long time" for light is still too small to notice in normal life.

    i.e.
    In a box 1m long, with mirrors either side, and assuming only back and forth reflection, any light inside will undergo 30000000 reflections in 1 second.

    If only 1/1000000th is absorbed/transmitted/lost in each reflection,
    in 1/100th of a second you have only 5% left,
    in 1/10th of a second you have 9x10-12% left.
    Get the idea?

    And that is without deliberately letting any out to, say, light a room.

    iirc: a bathroom mirror loses about 1% on each reflection
    polished silver gets you 0.1% losses and the best HR coatings can manage something like 0.01-0.001%.
     
    Last edited: May 16, 2014
  10. May 16, 2014 #9

    Simon Bridge

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    There are some more basic issues too:

    ... this is basically a skylight with a misleading name. The bottle of water is used as a lens and rough light-guide. It is not a light bulb.

    You seem to be thinking of one-way mirrors like you see on windows.

    If so: these do not work the way you seem to think - by being reflective only on one side and transparent from the other. They are usually partially silvered mirrors and let some light through in either direction, at all times. You see the mirror-finish on your side only if the other side is quite dark compared to the side you are on... so the reflection from the near side is much brighter than the light coming from the other side, so you only notice the reflection.

    This is why you can see inside the offices of mirror-glass buildings at night.

    That sort of mirror has losses, for your purposes, from 5-50%.
     
  11. May 17, 2014 #10
    Thanks for the info. I know how the Moser bottle is, by the way. Yeah, that's why I used the glasses. So that if it is brighter during the day, it lets part of the light in the box which stocks some of it by reflecting it inside. Then when it is dark at night, the light from inside should be visible, then. So if it traps some of the light, that is the 50-95% received, does it have chances of working if it is a partial vacuum inside?
     
  12. May 17, 2014 #11
    Thanks for the info. I know how the Moser bottle is, by the way. Yeah, that's why I used the glasses. So that if it is brighter during the day, it lets part of the light in the box which stocks some of it by reflecting it inside. Then when it is dark at night, the light from inside should be visible, then. So if it traps some of the light, that is the 50-95% received, does it have chances of working if it is a partial vacuum inside?
     
  13. May 17, 2014 #12

    Simon Bridge

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    No. No. No.
    The calculations I did assumed no losses to the air inside the box... i.e. a vacuum ...

    It sounds like you are not paying attention. Is it possible you do not understand the reasons that a mirrored box cannot be used as a light source?

    Even with impossibly near-perfect reflection, you lose all the trapped light in less than a millisecond - in microseconds you have too little light to be useful. The very best result you could get would result in just a flash of light when you go to use the box for illumination, and that assumes magically starting out with lots of light in the box.

    With the special glass proposed, you lose all the light even faster.

    What you propose is so far away from possible that it cannot be seen on a clear day with a really good telescope. Even magical properties won't help you so why do you persist?

    Maybe you'll just have to build one and see.
     
  14. May 17, 2014 #13
    Ah, ok. Thanks. So basically it won't work. Even with a partial vacuum. So I guess I'll just have to ditch it.
     
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