Model 3

Red roof in the rain

edited November -1 in Model 3
M3's roof is red when wet. Kinda cool to look at.... But why?
Can some physicist in the forum explain this phenomenon?
Thanks
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Comments

  • edited March 2018
    From jonnygozy on Reddit https://www.reddit.com/r/teslamotors/comments/81gzlj/tesla_rooftop_glass_is_gorgeous_in_the_rain/
    I'll take a stab at this.

    Basically, Tesla is putting a coating on their glass roofs that reflects UV and/or IR (probably both), but lets through visible light. This is called a dielectric mirror, or dichroic filter, or interference filter. It's made up of a number of thin, alternating layers of 2 materials with different refractive indices. You can tune the wavelengths that they reflect and transmit by changing the materials and thus their refractive indices as well as by changing the layer thicknesses.

    Normally, you can't really tell that there is a coating on the glass, as it is reflecting UV and IR, which you can't see, so it just looks like normal glass. However, when water (or some other liquid) is sitting on the surface of the glass, water has a different refractive index than air so it changes the optical properties of the coating and will then start to reflect different wavelengths.

    If I remember correctly, water should shift it to higher wavelengths, and thus a coating that was reflecting UV will now be reflecting in the visible (could have this backwards though - might be shifting to shorter wavelengths). In addition, dielectric mirrors have an angle dependence to them, so you will see different colors at different angles and thus the rainbow type effect. This is the same principle that makes those color shift pigments/paints work that you sometimes see on cars, printed on currency, etc.

    Hope this makes sense, let me know if I can clarify anything.
  • edited March 2018
    Thanks :) that was very educational. To me it's further proof that Tesla glass is working as it should.

    Now I'll try to oversimplify. Because I spend too much time making PowerPoints ;)

    Tesla uses glass that blocks UV and IR light. Under normal circumstances these invisible rays are refected back and we can't see them. A water layer on the glass alters the light properties to make it visible, this appears as shades of red to us.
    This also makes Tesla the coolest car to drive in rain :)
  • edited November -1
    That's interesting. I got to see it.
  • edited March 2018
    Thanks for that explanation. Now I FINALLY know what young Danny was talking about in The Shining.

    Red roof. Red roof. Red roof.
  • edited March 2018
    It looks great with a red car.

    https://imgur.com/bIiosxa
  • edited March 2018
    Cool! My car will look patriotic.
  • edited March 2018
    @Madatgascar: Awesome, thanks.
    @Coastal Cruiser: Amazing, how do people remember this stuff? I think these tidbits are the best part of the forums. More fun, less spitting contests.
  • edited November -1
    Look at a MX and you will see this effect. You will also see it on MS's that have the glass roof or Pano roof. I also notice that the windshield and rear window in my MS gives off a color that is not seen on the side glass..
  • edited March 2018
    Walked out this morning to frost on the car and freaked a bit when the roof seem to literally be glowing with different shades of the spectrum centered around red. It was very cool looking, and now I know why. Thank you for the info
  • edited March 2018
    To simplify, you can think of it as the oil slick effect. Some light will reflect off the surface of the water film and some off the boundary between the water and the first coating. These reflections will interplay with the reflections off each of the boundaries between the multiple coatings. Depending on the thickness of each layer the different frequencies of light will either reinforce or cancel each other. Apparently longer wavelengths are favored.
  • edited March 2018
    Thank you Professor Mann!
  • edited March 2018
    How does the it look from inside the car? Can you still see the effect / is it strange or distracting as a passenger/driver?
  • edited November -1
    No, no effect.
  • edited March 2018
    @jordanrichard, the Model 3's effect is much more vivid and pronounced than Model X. Check out this side by side comparison photo:

    https://imgur.com/Oya4AXl
  • edited March 2018
    And here's a close-up:

    https://imgur.com/RSMjZBx
  • edited March 2018
    Excellent to know. I was pleasantly surprised to see that during rain.
    Looks pretty awesome to me.
  • edited March 2018
    After seeing these photos I think there may be more going on than the thin film theory that we have been speculating about. The color changes even where the roof appears to be dry. Perhaps temperature is a factor.
  • edited December 2019
    Just guy a model 3 delivered in December.
    I don’t see the red color at all after rain/snow.
    Maybe the condition OSs not Right? Or Tesla changed the recipe out the coating?
  • edited December 2019
    “Just got” Sorry autocorrected.
  • edited December 2019
    only the early generation model 3s had this. Mine was delivered Aug 2018, only the roof glass had the red effect, the rear window did not have the same effect.
    My glass roof got cracked and tesla replaced it a few months ago and now the red effect is gone.

    If the red effect is truly due to UV/IR reflection then either tesla has gone away with that or gotten cheap.
  • edited December 2019
    Umm I’ll see when it’s summer.

    But the roof is quite darkly tinted from what I can tell.
    Didn’t get warm at all in the 1 day of sunshine during winter where the side windows are letting the warmth in
  • edited December 2019
    Late march 2019. Has orange/red roof. Only over front seats.
  • edited November -1
    @icenks: If there's one thing that roof window is, it's reflective of, not transparent to, infrared radiation. The idea is not to cook the car and overwhelm the air conditioning during the summer. So one is not going to see a green-house effect with that glass.
    I suspect that the side windows have similar treatment as regards the IR as the roof.
    It has been noted that some M3's with glass from different suppliers don't have the wet red window effect, so YMMV.
  • edited January 1
    Here's what it looks like with frost: https://imgur.com/a/8weeLrp
  • edited January 1
    @CclCal +1. Early ones had magic red glass from behind windscreen to the trunk.
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