Anti-glare sunglases and LC-Displays

Our friend Arild has a nice post in his own blog about the effects of using polarized sunglasses in combination with the HUD display of his 9-5.

As I also love my sunshades with polarized glasses, I would have loved if the HUD of the new 9-5 would behave the same way as the SID of my OG 9-5. Why am I comparing those different displays? Well they are both based on the same technology, namely LCD.

Thanks to Wikipedia, I don’t have to explain what the Malus’ law is. Nonetheless and in short, if the axes of two polarizing filters are orthogonal, the polarisers are crossed and in theory no light is transmitted.

Well a LCD screen uses the Malus’ law to let more or less background light pass through and show brighter and darker spots. And if the polarizing axe of our sunshades is orthogonal to the polarizing axe of the LCD, we will only see a black screen.

Coming back to the LCD’s in Saabs and other cars. I had a Citroen C2, in that car the information and radio Display was always pitch black when I had my shades on, I had to put my head almost horizontally to see something on that display. On the Peugeot of my wife it is almost perfect. If my head is vertical I see a darker display, but at least I see something. If I incline the head to one side the display gets darker, and if i incline the head to the other side the display gets brighter. But the best result is still the SID of my OG 9-5. Full brightness with my head in vertical position and dark display putting my head in a horizontal position, but I don’t usually drive in that position 😉

And what about the HUD? It seems like the polarizing axe of the display hasn’t been well chosen. Is somebody to blame? Not really, because the inclination of the windscreen might be the reason, but it is a problem that could have been corrected during the development of the HUD.

At the end of the day, new Saab should take care of such details, and I think they will.

15 thoughts on “Anti-glare sunglases and LC-Displays”

  1. Hi!
    I’ve notised this to. But only a tiny tilt is required. But as you say, this seems to be correctable.

    I’ve also noticed a small thing during my driving in (very) cold temperatures. The engine sound changes when the outside temp dropps.

    I take notes to self to find out the temperatures where this happends. But it is somewhere around minus 25 c.

    Note! This is a minor thing, the engine goes just fine and the car is a dream on icy roads.

  2. I don’t think you can ‘blame’ Saab for it. There are lots of sunglasses which don’t have that kind of glasses and still filter light very, very well. In fact, I bought Persol sunglasses, which are ten times better then Polaroid anddo not give such problems as mentioned in your post.

  3. Iirc correctly, light reflected from a surface is always polarized?! So, physically, since the HUD uses a mirror on the windshield, it will be completely up to the polarizing direction of the sunglasses. Saab can’t help this.

    And why did I believe that the SID was a Plasma display?

    • Thyl,
      I will check if I can black out normal light coming from a mirror, but I cant remember such effect at all.
      Well, I’ve decided to do it now, and I can’t black out incandescent light, no matter if the light beam comes directly to me, or if it is reflected on a mirror, sorry.

      And I don’t know why do you believe that the SID is a plasma display, At least I can do the black-out trick with the SID display of my Dame Redna, but I can’t do it with my Plasma TV screen.

      • Won’t happen with a mirror, it reflects all light regardless of orientation. Try light reflected at a shallow angle off clear glass.

    • Makes me wish I had some polarized lenses for testing. I think you are correct about the reflected light, at least from a transparent surface at an oblique angle (if I used the right word, and IIRC). However, our Aztek has HUD and I notice the reflective area on the windshield has a special reflective coating (this HUD requires a special windshield). I wonder if there is a way to solve this with a reflective coating that reflects all rays regardless of their horizontal/vertical orientation.

  4. I often wear “clip-on” Polaroid lenses attached to my glasses when I’m driving. I care about HUD ’cause my 9-5 (on her way home 🙂 ) will have it.
    I know that Saab tell about Polaroid dimming HUD light on the car’s manual.
    I think this is mainly due to phisical reflection on the windshield rather than being due to LCD.
    (Arild could try and confirm this by wearing Polaroid lenses, standing outside the car and looking from above the windshield directly into the “hole” containing the hud lcd…)
    Generally speaking, LCDs using circular polarization or keeping polarization at a 45° deg, can keep that problem to a minimum.

  5. You may wish to try on for size Serengeti’s “Polar PhD Drivers” sunglasses which are designed to circumvent the ‘LCD’ issue.

    Apparently, the underlying technology is used in military aircraft cockpits.

    I have an older generation of this lens (and no HUD equipped cockpit!) and they have proven to be the best driver’s sunglasses I have ever worn.

  6. This is only partially related, but I had the same issue with the GPS screen in the “older” 9-3. When I wore my sunglasses and tilted my head to the side – even just a little – the screen started getting dark.

  7. ’06 9-3 gps screen have the right polarization. It darkens only a bit when you are wearing polarized lenses and it darkens completely only if you tilt your head 45° deg left (or right, I don’t remember).

    Thanks for the advice, sorry they don’t have any “clip-on” lenses.

    • @Nicola, congratulations on your forthcoming HUD equipped 9-5!

      Tracking down ‘clip-ons’ might prove to be a bit of a challenge..

      From what I can gather, the 3rd party lens technology Serengeti uses is called “NXT Trivex” which is also licensed to other frame and lens manufacturers in a standard form (

      From the ‘Powered by NXT’ tab on their website, they list an American lens manufacturer called X-CEL Optical ( One approach would be to drop them a line and ask them which of their ‘customers’ produce ‘clip-on’ driving sunglasses with this lens technology.

      Alternatively, if you were to provide them with a ‘clip’ they may be able to affix the appropriate lens for you?!

  8. As a pilot and instructor of glass panel aircraft, this issue has been widely addressed. There are many sunglasses available that are not “polarized” the Serengeti drivers series and most “driving” lenses do quite well.

  9. I’ve driven now about 20 000km’s on new 9-5 with HUD and always when it’s been sunny I’d used my polarized Oakley’s. I’ve found the HUD to work superbly with polarized sunglasses. I do need to turn the “dim” on the HUD up a bit, but I’ve thought that’s due to the tint on the sunglasses, not due to the polarization. Nevertheless I’ve had no issues whatsoever with polarized sunglasses together with the new 9-5 HUD. I’ve had issues with other car brands with their incorrect polarization, but none in any Saab’s and it remains the same with the new 9-5. Could it be that you should choose your sunglasses better?

    Greetings from Finland. 9-5 works great in the winter conditions we have, -25 celsius today and no problems whatsoever. (Although the HUD needs to warm up in the morning for couple of kilometres, but that’s no biggie)

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