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Jun 18, 2023 at 18:22 vote accept Petr
May 30, 2023 at 0:07 history protected CommunityBot
May 29, 2023 at 22:43 comment converted from answer user368488 I see these spots on other cars and my car. I also bought a new 1976 chevy that had the same spots.
Jun 16, 2022 at 11:31 comment added Solomon Slow Re, "the pattern is much more visible when viewing a reflective surface" That's because the reflected light is polarized. en.wikipedia.org/wiki/Specular_reflection#Polarization You effectively are viewing the car window through a crude polarimeter. The "reflective surface" functions as the polarizer, and your sunglasses function as the analyzer.
Aug 18, 2016 at 23:30 answer added Brice timeline score: 6
Aug 10, 2016 at 1:26 history tweeted twitter.com/StackPhysics/status/763184671257718784
Aug 9, 2016 at 13:12 comment added Petr @WetSavannaAnimalakaRodVance +1 to not dying. The picture was taken during a trafic jam when cars were standing still.
Aug 9, 2016 at 12:51 comment added Selene Routley Grand experimental question by the way. I've noticed this many times in my 52 years and now ashamedly realize my inner nerd was never lured by this particular effect I (and I have significant optics training BTW); I guess one's mind is a bit distracted by the aim of not dying in a horrible road accident when driving - I can't otherwise think why I've never thought about this!
Aug 9, 2016 at 12:47 comment added Jim @WetSavannaAnimalakaRodVance Yes, I was kind of hinting that Brewster's angle would play into it that way, but also I was providing the link for further reading on a related phenomenon
Aug 9, 2016 at 12:41 comment added Selene Routley I think what @Jim means is that the light reflected from the surfaces like other car windows and the like becomes partially polarized owing to difference between the reflexion co-efficients for each polarization state (as described by the Fresnel equations) (Jim, hope I'm not misthinking you). The partial polarization then lets you see the effect noted by curiousStudent. I don't know anything about safety glass, so I don't feel I can answer but I'd wager a significant sum on the answer given by curiousStudent in the light of Jim's comment as being the answer, if I were the betting kind.
Aug 9, 2016 at 12:15 comment added Jim for further info, also read up on Brewster's Angle
Aug 9, 2016 at 12:13 comment added curiousStudent From Quora: "These spots are caused during the tempering process. They are intentional stresses which are created in the glass to make it stronger and to control the way it breaks in an accident. The result of this is that it breaks into thousands of small pieces instead of as few large knifelike pieces. The internal stresses can be seen under polarized light or through polarized glasses. The pattern of spots reflects the arrangement of heating elements or flames which are used to apply the heat. "
Aug 9, 2016 at 12:10 comment added Petr @curiousStudent Yes, IIRC the grid appears to be stationary wrt the rear window.
Aug 9, 2016 at 12:10 comment added curiousStudent If you move your head around, does the grid appear to be stationary?
Aug 9, 2016 at 12:06 history asked Petr CC BY-SA 3.0