X-33 LCD Display - Circular Polarizer? X-Post

[gaijin]

It was suggested in the Omega forum that I re-post my question here, so here you go:

Originally Posted by gaijin

Still learning about my new X-33 - sounds like an excuse for a gratuitous pic:



While driving around today, I noticed that the LCD display was perfectly legible AT ANY ANGLE while wearing polarized sunglasses.

This is much different than other LCD displays viewed while wearing polarized sunglasses which will "black out" when viewed at certain angles.

When I returned home, I took a polarizing filter and held it in front of various LCD display watches and rotated the filter - in every case, EXCEPT THE X-33, the display would "black out" at a certain angle. My Suunto Core, all my G-shocks, Seiko "Arnie," etc. all "blacked out."

The fact that the X-33 LCD display does not "black out" is very significant, IMHO. Significant enough to at least mention in the various reviews and specs I have read, but I have found no evidence of this feature anywhere.

But how is this possible? Do Omega use a circular polarizing layer in the LCD display? Anyone know?

.

[Eeeb]

The 'blacking out' when using a polarizing filter comes from the reflection being polarized. It is possible the anti-reflective coating interferes with this phenomena.

I doubt the G-shocks has an anti-reflective coating... could it be the others don't either?

[M4tt]

I'm pretty sure that the AR effect is achieved by coating the sapphire with a material which has a refractive index about half way between that of air and that of sapphire. (Actually; it is far, far more complicated than this, but this is close enough without being boring.) This minimises the irritating boundary effects.

I'm not really sure if there is a material available that combines this effect with polarisation. I suspect a polarised crystal would be both very obvious and irritating.

[gaijin]

I don't believe the AR coating on the crystal has anything to do with this phenomenon.

A Liquid Crystal Display (LCD) is a sandwich of glass with a display layer and a polarizer layer. Without the polarizer layer, the digits on the display would be unreadable.

You can see details of how a "positive" (black letters/numbers on a light background) LCD display can be changed to a "negative" (light letters/numbers on a black background) by rotating this polarizing layer 90 degrees in some previous G-shock "how-to" threads.

The "black out" phenomenon observed on watches other than the X-33 is limited to the LCD display area only - not any watch crystal which may cover it.

Anyone know if the LCD's on the Breitling B-1 are also immune to this phenomenon?

Seeing as how pilots would be likely to wear polarizing sunglasses, I would think this would be good to know.

Any further thoughts?

[Wytnucls]

Originally Posted by gaijin

Seeing as how pilots would be likely to wear polarizing sunglasses, I would think this would be good to know.

Any further thoughts?

Just a small correction: Commercial jet pilots don't wear polarizing sunglasses, as they affect normal vision through layered glass heated windscreen panels.

[gaijin]

Originally Posted by flyinghell34

Hey gaijin,

Now what did I say. These guys got all the answers.

BTW. Great X-33. Love mine as well.

John

Maybe I'm missing something, but I don't see an answer yet ...

[Eeeb]

Yeh, but the discussion exists... we haven't given up yet!

[Fatpants]

Why not get in touch with Omega and see if they can give a definitive answer as to what they do to the module in order to overcome the effect of "black out"?

[Eeeb]

Yes... and I would like to see another X-33 owner confirm the behavior. I'd do it but I have yet to find one I can afford

[Fatpants]

Originally Posted by Eeeb

Yes... and I would like to see another X-33 owner confirm the behavior.

I'll give it a go tomorrow and let you know

[gaijin]

Originally Posted by Fatpants

I'll give it a go tomorrow and let you know

While you're at it, try a Breitling B-1 if you have one - I'm curious to find out if it also is immune to this phenomenon.

.

[eurocopter]

gaijin, I think you are right. I'm not an expert or anything, but there are probably 2 normal linear filters, one behind, one in front of the glass layer angled at 0°. On top of that, there is a quarter-wave plate that transforms linearly polarized light passing through the top linear filter into circularly polarized light. Circular polarization eliminates phase & angle variations, so when looking through additional linear filter (glasses) there is no effect.

[gaijin]

Originally Posted by eurocopter

gaijin, I think you are right. I'm not an expert or anything, but there are probably 2 normal linear filters, one behind, one in front of the glass layer angled at 0°. On top of that, there is a quarter-wave plate that transforms linearly polarized light passing through the top linear filter into circularly polarized light. Circular polarization eliminates phase & angle variations, so when looking through additional linear filter (glasses) there is no effect.

Thanks, eurocopter, sounds pretty good. Does that mean, however, that ANY LCD could be "made" immune to blackout by layering a circular polarizer over it?

The only circular polarizer material I have is part of a two-part camera filter designed to be used with certain pellicles on SLR's and I cannot separate the two layers to try it out.

[kairos]

I too have noticed the polarizing effects on the X-33, but what I have seen is that the display DOES black out when oriented in a certain way relative to my polarizing sunglasses. What impresses me is that the polarizer in the X-33 LCD display is rotated so that with one's hand at about 10 o'clock on a control yoke (or steering wheel), the polarizer in the display is oriented so there is no attenuation of the digital display when wearing sunglasses. This could hardly be accidental. With my 2nd gen X-33 (no longer in the stable, sadly), rotating my wrist to a horizontal position (or a more vertical position) DID cause polarizing attenuation. I can't explain different results that others have seen. Is it possible that Omega has used different configurations of the LCD display? Comments already made noting that pilots don't use polarizing sunglasses are very much appropo--but it seems that Omega's engineers were thinking of situations beyond piloting in designing the watch.

[eurocopter]

Originally Posted by gaijin

Does that mean, however, that ANY LCD could be "made" immune to blackout by layering a circular polarizer over it?

I think so, but can be wrong. I don't have any photo lens filter so I can't try it, but you can. Simply try to put your camera filter over a G-Shock for example. If you put it inner (circular) side down and rotate it what happens? If nothing, the theory is right. You don't need polarization glasses since there already is linear polarization layer on filter top (filter outside).
Then try to flip it and rotate. It should go dark when the linear layers are at 90°. Try it and let us know.

[gaijin]

Originally Posted by kairos

I too have noticed the polarizing effects on the X-33, but what I have seen is that the display DOES black out when oriented in a certain way relative to my polarizing sunglasses. What impresses me is that the polarizer in the X-33 LCD display is rotated so that with one's hand at about 10 o'clock on a control yoke (or steering wheel), the polarizer in the display is oriented so there is no attenuation of the digital display when wearing sunglasses. This could hardly be accidental. With my 2nd gen X-33 (no longer in the stable, sadly), rotating my wrist to a horizontal position (or a more vertical position) DID cause polarizing attenuation. I can't explain different results that others have seen. Is it possible that Omega has used different configurations of the LCD display? Comments already made noting that pilots don't use polarizing sunglasses are very much appropo--but it seems that Omega's engineers were thinking of situations beyond piloting in designing the watch.

Originally Posted by eurocopter

I think so, but can be wrong. I don't have any photo lens filter so I can't try it, but you can. Simply try to put your camera filter over a G-Shock for example. If you put it inner (circular) side down and rotate it what happens? If nothing, the theory is right. You don't need polarization glasses since there already is linear polarization layer on filter top (filter outside).
Then try to flip it and rotate. It should go dark when the linear layers are at 90°. Try it and let us know.

Kairos, I cannot explain why we have seen different things, either

Let me try to show you what I am talking about by using a polarizing filter, a Suunto CORE (nice, large LCD watch) and my X-33 Gen2.

First, a picture of the CORE:



Now a picture of the CORE with a polarizing filter in front of it oriented at 0 degrees (note white tape at 12 o'clock indicating orientation) which causes no blacking out of the display:



And a picture of the CORE with the filter oriented at 270 degrees showing how the display turns totally black rendering it illegible:



Compare this to pictures of my X-33 Gen 2 with the polarizing filter at 0 deg, 90 deg, 180 deg and 270 deg with no blacking out of the display - you will just have to trust me (or try it yourself) that no orientation of the filter caused any "blackout."

First, my X-33 by itself:



X-33 with polarizing filter at 0 deg:



X-33 with polarizing filter at 90 deg:



X-33 with polarizing filter at 180 deg:



X-33 with polarizing filter at 270 deg:



I have tried this with Casio, Seiko and Citizen LCD watches and they all black out like the Suunto.

The X-33 is the only watch I have experienced that remains legible.

Does this help?

[eurocopter]

Great pictures gaijin, thanks. So the theory goes to dumpster.
And you tried to flip the filter on the Core, right? Both sides the same effect?

[gaijin]

Originally Posted by eurocopter

And you tried to flip the filter on the Core, right? Both sides the same effect?

Yes. 90 deg and 270 deg both blacked out the display on the CORE, while 0 deg and 180 deg both had no effect.

[Bruce Reding]

Excellent work, gaijin!

[Bruce Reding]

Sorry for the late entry into the discussion (my son graduated yesterday ), but the first fifteen years of my career had a high content of optical physics. As such, I can help with the discussion.

As this wiki article explains, the top layer of an LCD display is a linear polarizer. (It's one of two in the display.) This means that the light leaving the display is linearly polarized. As such, if it goes through another polarizer (your polarizing sunglasses, for instance), and if there is a nonzero angle between the polarization of the emerging light and the axis of the sunglass's polarization acceptance, then the light from the display will be diminished. This diminishment will vary sinusoidally as a function of the angle, and will be substantially 100% when the two are at 90 degrees relative to each other.

Now, as it turns out, the polarizers in polarizing sunglasses always have the same orientation. Simplistically, they're oriented to block horizontal glints (direct reflections of the sun), which, due to Brewster angle effects, can be highly polarized. Evidently, lcd manufacturers are aware of this systematic orientation of the polarization angle in sunglasses, and choose to orient their polarizers such that the light emerging from their displays is polarized at the same angle. Therefore, the sunglasses do not further block the display.

The downside of this simple solution, as gaijin picked up on, is that if you place the two at ninety degrees from the typical angle that they design for, then the sunglasses "black out" the display. Note that this black out will only occur for the display, as the ambient light (that which is illuminating the case, etc.) is not polarized. As such, the watch and all around it remains perfectly visible. It's just the display that blacks out.

A better solution for this is to change the light emerging from the display so that it's no longer linearly polarized. As eurocopter noted, this can be accomplished by changing the polarization from linear to circular. This is done by adding one more element -- a quarter wave plate. This is a birefringent material that, if oriented at 45 degrees to the emerging light, and if of the appropriate thickness, will change the light from linear to circular. The latter has no orientation. so will interact with the polarizing sunglasses in the same way no matter the relative orientation of the two.

One could recreate this effect in gaijin's experiment by placing a circularly polarizing photo filter at 45 degrees above the Suunto's display. Re-doing the experiment with this setup would yield results similar to those for the Omega.

Quarter wave plates cost money, of course. As such, Omega should be commended for such a thoughtful design adder. Also, gaijin should be commended for noticing this excellent design feature.