Sunglasses and the HUD

[uraniumrich]

I'm a little confused by that -- they mention that both the projector and the windshield cause polarization, but they've only addressed the projector end of things? You's still have to come up with a way to keep the reflected image from being polarized.

I read through the article and it does a nice job of simplifying the science behind polarization. A HUD takes advantage of the partial reflection of light by the windshield. Some of the light from the screen mounted in the dashboard is reflected off the windshield and back at the driver. The screen mounted in the dashboard is an LCD screen which emits polarized light. So, the light reflected back at the driver is also polarized (meaning that it is all oriented in the same direction.) Polarized sunglasses have thousands of tiny lines which are oriented vertically. If the light emitted by the LCD screen is not polarized with the same vertical orientation, then it will not pass through.

The simplest analogy is to think about looking through two picket fences. If you have two fences which are both oriented vertically (0 degrees from each other), then you can see through them. But, if one fence is oriented vertically and the other is oriented horizontally (90 degrees from each other), then you wouldn't be able to see anything. Any orientation between zero and 90 will reduce the amount of light, but still allow some to pass through. If you try rotating your head when you are wearing polarized glasses, you will see this effect because the HUD will get brighter/darker depending on the orientation of your glasses compared to the HUD.

Hope that helps a bit!

 

[Reidog]

At first, I couldn’t see HUD wearing polarized sunglasses but I noticed when I had my front windshield tinted with a clear UV protection with a slight blue tint to it, I can see the HUD now with my polarized glasses.

 

[ultane]

At first, I couldn’t see HUD wearing polarized sunglasses but I noticed when I had my front windshield tinted with a clear UV protection with a slight blue tint to it, I can see the HUD now with my polarized glasses.

That must be why my HUD is perfectly visible with my polarized Wayfarers as well. I had every glass surface in Miss Daisy tinted with ‘ceramic’ window tint on day two or three of ownership.

 

[bluebullet]

Yeah, polarized glasses I guess do it. My Maui Jims are doing it.
I should say, was doing it. I just got my windshield tinted 35% and now I can read it clearly.

Nick, it bothers me that I understand your signature line...

 

[Colin_MKV]

Its like this is all cars with HUDs. Being said I enjoy when I hop in at night and am like "woah i totally forgot i had that feature"

 

[Markarian421]

I read through the article and it does a nice job of simplifying the science behind polarization. A HUD takes advantage of the partial reflection of light by the windshield. Some of the light from the screen mounted in the dashboard is reflected off the windshield and back at the driver. ...

The part I don't understand is that even if the light from the projector was unpolarized, using the windshield to reflect the light will polarize the light -- to a greater or lesser extent, depending on the angle, but still the same problem for most useful angles of reflection.

You can see on that plot, over most of the range of angles reasonable for reflecting an image, you're going to get a very polarized image with nearly none of the vertical polarization being reflected. They'd have to push the reflection off the windshield to a really high angle maybe?

Source for the plot: Methods for Producing Polarization