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Window reflection when dark out side act like mirror

  1. Sep 18, 2015 #1
    Why is it that when a light is on in a room with a window made out of glass, and it being dark out side the window. That you cannot see through the window and instead see light being reflected form the room around you. And vice versa when it is darker inside the room and brighter out side you can not see into the window form outside. Why is this that the window becomes more like a mirror when there is no light coming form behind it.

    As well if there is equal brightness or amount of photons on both sides do you get equal visibility on each side?
  2. jcsd
  3. Sep 19, 2015 #2


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    The window always reflects some of the light. It is just that when one side is dark the reflection is more visible because it does not have to outshine the light from the other side to be seen.
  4. Sep 19, 2015 #3


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    The glass reflects about 4% of the incident light and transmits 96%. If there is equal visibility on both sides, you will see the transmitted light. If there is very dark outside, so as the incident light from outside is less then a percent of the incident light from the room, you will see your mirror image.
  5. Sep 19, 2015 #4
    yes, basically when it is dark outside (very little light transmitted through the window) you can notice the small amount of light reflected off the window. Whereas if it is daylight out the light transmitted is much larger than the light reflected off the window so the reflected light can not be detected (it is buried in the transmitted light, so to speak).
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