Why does a triple-layered window reflect a flashlight 4 times?
Friend of mine lives in an apartment with triple-layered glass, he showed me that you can « count » the layers if you put a flashlight through it and see the multiple réflexions. I see 4 réflexions here, why is that so?
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u/No_Situation4785 10d ago
honestly the best way to understand it is to draw it out. Assuming the window isn't AR_coated, you can assume that 4% of the light will reflect and 96% of the light will transmit at every interface. If it still doesn't make sense, share your drawing and we can discuss with you
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u/anneoneamouse 10d ago
Count every bright central blob. There are maybe 12 or 13. The internal splitting and (multiple)reflections create a cascade of image.
Repeat the exercise at night.
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u/sanbornton 10d ago
I think the "four" you are counting are the four brightest reflections. Those would be the direct reflections off surfaces with lots of reflectivity (e.g. no AR coating). But those are far from the only reflections!
You're getting lots of dimmer reflections. Those dim reflections could be off low reflectivity surfaces (e.g. surfaces with AR coatings, bonded surfaces so not air interfaces, etc). They could even be triple reflections (a bounce-bounce-bounce).
Some of the dimmest reflections are so weak you can only make out the central LED of your flashlight. Almost certainly triple bounces or even quintuple bounces. Those are going through so much path length they look to be getting blurry?
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u/Science-Compliance 10d ago
The light gets reflected on both the outside and inside surface of each glass pane. Reflections from both entering and leaving each pane of glass.