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So, the yellow-green spots in the upper-right corner of this image are my camera's indicator light reflecting off a double-pane glass window. The bright spots are direct reflections, while the dimmer ones are the result of multiple reflections off the layers of glass. But why are there four bright spots? Shouldn't there be only two, one for each air->glass transition?

  • $\begingroup$ I mean, no. Supposing you point a mirror at a mirror, you don't get just two reflections between them. There should be a first reflection from the front pane, a second reflection from the back pane, a third reflection from the back pane which has reflected off of the front pane and then reflected off of the back pane. What's surprising is that the 4th and 5th are almost as bright as the 1st and 2nd reflection. That suggests something more like a storm window or a better-energy-efficiency window where there can be multiple layers and therefore multiple primary refractions. $\endgroup$ – CR Drost Dec 17 '16 at 5:08

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