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Question about reflecting sunlight off a mirror

  1. Apr 24, 2006 #1
    First off, I apologise for this basic (and rather random) question. I am not educated in this area, in fact I have no education in physics whatsoever, but an idea for an invention came to me over the weekend and whether it is feasible or not depends on the answer to this question. I have enjoyed reading these forums before and thought this was a good place to try and find an answer.

    Here goes:

    If I hold a flat mirror at an angle outdoors and direct the sunlight against a wall, it appears on the wall in a similar shape and size to the dimensions of the mirror I am reflecting it off. My question is, is it possible - perhaps using a mirror with a rounded edge - to create a beam of sunlight larger than the surface area of the mirror I am reflecting it off? If so, what shape and properties would a mirror need to have in order to divert the sunlight off it and create a ray of light with a much larger surface area than that of the mirror itself? Is this possible without breaking the light into lots of smaller rays in the way a mirrorball does?

    Many thanks for any input, and thanks for bearing with me!
  2. jcsd
  3. Apr 24, 2006 #2
    Try concave or convex mirror

    The sunlight will bounce off the mirror at the same angle it strikes it, If it arrives at 90degrees it leaves at the same angle, if it arrives at 45degrees it leaves at that angle. In order to produce the result you are aiming for you require a curved mirror so that the sunlight strikes each part at a slightly different angle and deflects in an arc.
  4. Apr 24, 2006 #3


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    As Tzemacvh points out, a mirror that is convex will reflect a diverging beam i.e. you will get a larger spot on the wall than the size of the mirror.

    Since you mention an invention, I'll jump ahead and guess where you're going. That spot of light on the wall, in addition to being larger, will also be proportionally dimmer. You don't get any more energy just because the area is larger.
  5. Apr 24, 2006 #4
    Thanks for posting guys.

    Looks like my idea wouldn't work then.

    The idea came when I was enviously looking out of my window at some neighbours basking in the sun in their conservatories late in the afternoon, at which point there was no direct sunlight on my garden. I wondered whether it was possible to turn my lounge into a conservatory using specially made mirrors situated outside of the house and diverting the sunlight into the house.

    It would seem my invention has fallen at the first hurdle!
  6. Apr 26, 2006 #5


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    Oh - you could definitely do that! No trouble!
  7. Apr 26, 2006 #6


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    Staff: Mentor

    Yeah, you can absolutely redirect sunlight. You'll need a pretty large mirror to deflect enough light (roughly the size of the target area). I recently saw on one of the nature or travel shows, that a small village someplace at the bottom of a steep valley was installing a bank of mirrors at the top of the valley to give them some more sunshine.....
  8. Apr 27, 2006 #7
    Great, the idea's not a dead one then! Just need a large mirror. But it would have to move gradually throughout the day to enable the sunlight to stay on target...

    Sounds a bit tricky.
  9. Apr 27, 2006 #8
    You can also increase the amount of light/heat arriving by focussing several mirrors onto the same area - but be careful. Depending on where you live and the amount of heat already available you could cook your dinner with half a dozen mirror tiles.
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