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Light through out the home without switch being on for all the time.

  1. May 10, 2014 #1
    Optical fibres are used to transmit light from one place to the other along curved path in a more effective manner. The optical fibres consist of thousands of strands of a very fine quality glass or quartz of refractive index about 1.7 or so. The thickness of a strand is about 10-6cm. The strands are coated with a layer of some material of lower refractive index (about 1.5). The ends of the strands are polished and clamped firmly after aligning them carefully. When light is incident at a small angle at one end, it gets refracted into the strands (or fibres) and gets incident on the interface of the fibres and the coating. The angle of incidence being greater than the critical angle, the ray of light undergoes total internal reflections. It suffers internal reflection again and again.

    If we consider fibre in circular shape (fibre image is not in circular shape) and incident light at the angle greater than critical angle from one part of that fibre, light undergoes total internal reflections without being absorbed, so we can have the same light circulating all the time.

    1.Suppose if we have the planning of home to be made in the same manner of the circle shaped fibre with same material as that of quartz. We can have same light circulating all over once incident. So, if this happens we can have light through out the house with out light being switched on for all the time. Is this possible?

    2.I know there might be some difficulties which might arise, if so what are they? What can be done in order to over come those?
  2. jcsd
  3. May 10, 2014 #2


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    Why do you think we don't have to switch on the light source(That LED for example) all the time?

    Light travels very fast.So if you switch off the light on one side of the fibre,light would stop reaching the other side immediately.

    EDIT: I think I now understand what you are trying to do.
    Yes. If the light is reflected perfectly,with no energy loss, it will go through out the fibre for eternity.But that's not possible in real-life.

    Again,there will be energy loss if you let the light go out of the fibre(Assuming that the fibre is perfect),which is what you are trying to do!
  4. May 10, 2014 #3


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    Light scatters, and is absorbed ... so only some of the previous output will reenter the fiber for the next loop.

    Suppose that your system is 99.99% efficient, and that a complete loop about the house takes 200 meters ... since light travels about 200,000,000 meters per second in fiber with an index of 1.5, this means about 1,000,000 round trips for the light each second.

    Now calculate (0.9999)^1,000,000 ... this is the amount of light left in the system after 1 second.

    The Google calculator says it's 3.7015208e-44; for all practical purposes this is the same as zero!

    In reality optical fibers also have losses - that is why they match the wavelength of the signal to the lowest loss of the fiber for optical communications. Even under the best of circumstances the signals must be regenerated every 100 kilometers ... in your case this corresponds to once each 500 loops, or about 2,000 times per second.

    Thus from an engineering point of view such a system would not meet your expectations.
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