
Humans can sense the polarization of light with the naked eye - davesailer
http://blogs.discovermagazine.com/crux/2015/07/01/sixth-sense/#.VZRESKbTHKM
======
mutagen
Researchers suspect that Vikings used this effect in combination with a
'sunstone' (Icelandic Spar) to navigate by the sun even when it was hidden by
clouds.

Article: [http://news.discovery.com/earth/navigating-by-sunstone-
and-a...](http://news.discovery.com/earth/navigating-by-sunstone-and-a-sixth-
sense.htm)

Paper:
[http://rspa.royalsocietypublishing.org/content/468/2139/671](http://rspa.royalsocietypublishing.org/content/468/2139/671)

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modeless
Fascinating! Wikipedia has a great illustration of what it looks like, and now
I can definitely see it in my LCD monitor.

[https://en.wikipedia.org/wiki/Haidinger's_brush](https://en.wikipedia.org/wiki/Haidinger's_brush)

~~~
cjslep
> Haidinger's brush may also be seen by looking at a white area on many LCD
> flat panel computer screens (due to the polarization effect of the display),
> in which case it is often diagonal.

Thanks for that, I thought there was something wrong with me when I saw my
yellow bow-tie neither perfectly vertical nor horizontal.

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dsrguru
Took me an hour but I got it! Staring at a solid background on my Nexus 5 on
full brightness in a pitch black room did the trick. Horizontal linear
oscillation was more noticeable for me than vertical for some reason, which
meant holding my phone in landscape mode. The brush pattern is significantly
fainter on my laptop than my phone, and I seem to lose the effect every few
minutes when using my laptop. I've been able to bring it back by glancing back
at my phone in landscape. This is really, really cool by the way.

~~~
steve19
After an hour of staring at a white LCD screen,I think you will see whatever
your brain wants you to see ;-)

~~~
dsrguru
Nope it's very clear once you know what to look for, as long as you're looking
at something highly polarized. I still have this superpower about five hours
later.

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DEinspanjer
So after a little owl-like head twisting, I was able to perceive the brush on
both of my Dell 24" LCDs. However, I noticed something interesting.

Even though they are fairly similar models with a year or two difference
(U2410 vs 2408WFP), they have different polarizations. The U has a vertical
brush/bowtie and the WFP has a horizontal brush.

In the past, I have noticed that the brightness of the two is different and
has been hard to match. If I drag an application between the two screens, it
is almost impossible to tune either monitor so the display is uniform.

Does the manufacturer explicitly determine the orientation of the
polarization? Are there reasons for one versus the other? Reasons why a
manufacturer might want to rotate it?

I have noticed in the past that some dashboard or nav screens in cars are hard
to see with my sunglasses while others aren't, and I know that is due to the
orientation of their polarization because if I twist my head 90 degrees, the
effect reverses.

Fun stuff.

~~~
TheAdamist
If you have polarized sunglasses you should be able to verify those
polarizations by rotating your sunglasses to see when the screens go black vs
look normal.

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pjungwir
I've never understand the idea that in non-polarized light, the "amplitude" of
the light wave points in all directions, whereas in polarized light it points
in only one. The amplitude of a light wave doesn't literally mean something is
oscillating up and down, right?? The amplitude is just the light's intensity.
So what does it really mean for light to be polarized? And why do thin slits
cause polarization?

~~~
abdullahkhalids
Light is an electromagnetic field: a wave-on-a-rope type thing except the rope
is space. An electromagnetic field exerts a force on charged objects like
electron, protons or even entire atoms and molecules. If you put an electron
and shoot polarized light at it, it's movement will be consistent with the
electric field going up and down in a particular plane. Analogously for
unpolarized light.

A thin slit cause polarization the same way only one plane of oscillation is
possible for a rope passing through a slit. Except what is stopping the
oscillations in 'bad' directions is the interaction between the
electromagnetic field and atoms that make up the boundaries of the slit.

~~~
pjungwir
Thanks! After reading this [0] I'm surprised that my high school recollection
seems to be how it really works. It still seems very strange. One thing in
that article bothers me though: it talks about the wave itself as vibrating,
e.g. "A light wave that is vibrating in more than one plane is referred to as
unpolarized light." But how does a wave vibrate? It seems like a sloppy use of
language. Using your own words maybe it's more correct to say that space is
vibrating? Or rather vibration is just a metaphor for the EM field?

[0]
[http://www.physicsclassroom.com/class/light/Lesson-1/Polariz...](http://www.physicsclassroom.com/class/light/Lesson-1/Polarization)

~~~
ars
It's more the 2 fields that are vibrating.

The "length" of the photon is very short. There is not a long wave like you
are thinking, like a wave on a string.

Take a short string and pull it over a sine wave. At any instant in time, one
part of the string will be high, another part low. As you pull it, the
position changes, but the sun total of all the "heights" in the sine wave is
always the same, no matter what part of the sine wave you start at.

So you can think of a photon like that: As it snakes it's way through space,
it doesn't actually move up and down, but rather as it progresses the front of
it will sometimes be "high" and sometimes "low".

Take a hose and wave it in the air, to make a sine wave of water. Now think of
each molecule of water - every single molecule only moves forward in a
perfectly straight line! None of them move side of side. Yet it looks that
way, but it's really new molecules, some of them are moving here and some
there.

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ridgeguy
Used the white screen at

[http://www.ledr.com/colours/white.htm](http://www.ledr.com/colours/white.htm)

Can see faint blue & yellow bow tie figures as the article describes on my
laptop LCD. They change as I rotate the screen. Very interesting.

~~~
throwaway_97
I cant see any bow ties :/

~~~
colordrops
Maybe it depends on the screen type. I can see it very clearly on my macbook
LCD screen, but I can't see almost anything g on my Samsung S4 OLED screen.

~~~
ars
> OLED screen.

Right. I would not expect it with an OLED since that is not polarized.

------
jrapdx3
Very interesting. Didn't take too long before seeing faint yellowish blobs.
The only problem was tilting my head too fast, made my neck joints creak.
Slowing down was better, it didn't take more than modest offset (say 25
degrees) anyway once knowing what to look for.

It worked differently on two computers. One is a fairly recent MS Surface Pro
2 tablet, the other an ancient Dell D630. The display on the Dell is TN, and
not as blue as the IPS screen of the SP2. The effect was a little easier to
evoke with the Dell, though its screen color made the yellow less distinct but
the blue counter-color more visible.

Occasionally I experience aura of migraine, in one form appearing as blobs of
color moving around the visual field. (Not necessarily yellow, can be any
color.) Maybe it's a reason I've never noticed the polarization effect before,
the faint yellow/blue spots just got lost in the noise.

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scoot
Oh, wow, I got it without even trying just by rotating my laptop screen 90
degrees (portrait vs. landscape if that make sense.) with just a web browser
on this HN page (no other white screen needed).

I'm sure I've noticed this effect before, as I often stand my laptop on its
edge on the floor like an open book when I'm not using it (easier to reach
down and grab the body that way), but hadn't paid it much attention and had no
idea of the cause.

Retina MBP if that makes a difference.

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whoopdedo
Since 3D movies use polarized light, could this contribute to the nausea some
people experience when watching them? Or is that just the fast movement (like
video games) since nearly all 3D movies are action films.

edit: I now remember that 3d movies are projected using radially polarized
light. The article only describes linearly polarization. There's also spiral
and azimuth. Polarized light is really complicated.

~~~
fishanz
Yeah; I'm curious if there is anything comparable to this for radial
polarization.

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wcchandler
I wonder if this contributes to eye strain and brain fatigue.

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amelius
Couldn't it be the case that the human eye is just sensitive to the artifacts
of a polarization filter?

~~~
rcthompson
Not if it also works on polarized light in the sky.

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evincarofautumn
Huh. I thought all humans could see polarisation.

Further evidence that I should stop presuming other people are like me.

~~~
bitJericho
I had no idea this was possible, and had never seen this effect. Of course I
launch a blank screen on my phone and the effect is plain as day, I don't even
have to tilt my head back and forth. Amazing!

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benihana
> _To see Haidinger’s brushes for yourself, look at a blank white portion of
> an LCD screen on a computer, tablet or phone._

Holy crap, it worked! They're very very very faint, and if your monitor ins't
clean, they're easy to miss. They appear right where you're looking at. If you
imagine two lines coming out of your eyes at the screen, they show up right
where the lines converge. Very faint and pale yellow, almost looks like a
fading after-image.

Only saw them when I rolled my head left and right / up and down. Imagine
pointing one ear towards the floor and the other towards the ceiling - I
oscillated between these two positions and saw it.

It was harder to see when I unfocused my eyes like I was going to look at a 3D
picture. Easier to see when focusing on the spot in the screen I'm looking at.

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MichaelCrawford
I have long noticed this effect however I had no clue I was seeing
polarization.

I'm into photography. I had a dead-simple Pentax K-1000 SLR. Its only
automation is a very basic light meter; I adjust the aperture and exposure
until the needle is where I want it to be (ie. sometimes purposely over- or
under-exposed).

Three lenses, but with a polarizing filter for each. Mainly I use the
polarizers to deepen the blue of the sky.

~~~
spydum
Same here.. I have been on occasion caught staring off into a blank editor
with white background and just assumed the yellow was some eye strain related
thing.

Also..totally agree and I do the same: Circular polarizer for camera can ineed
make some cool cloud/sky photos without drastically affecting the rest of
frame.

------
mikeiwin10
thanks for sharing

~~~
yoha
Hackers News tend to prefer messages that contribute something new to the
conversation. This is why users downvote most jokes and often even positive
comments such as yours, that should have simply been an upvote of the post.
However, you seem new (green user name), so that's understandable the first
time.

~~~
jwdunne
I like this. Familiarising newcomers to the community's ways as opposed to a
blind downvote is a good way to welcome them.

We must remember that these sorts of posts are acceptable on other discussion
forums, news aggregates and 99% of social media as a whole. Many newcomers
will be used to this freedom and may feel intimidated because their first post
received a -- in karma, without knowing it's won as easily as it's lost.

I, personally, comment very irregularly. I hold myself to a strict rule of
only commenting when I feel I can add real value to the discussion - on a lot
of subjects, experts way above my skill level do this so I do not comment.

~~~
kleer001
Seems to me that someone could write a bot to chaperone newbs until they got
to a certain level of community standards.

~~~
jwdunne
In true hacker spirit, we could use ML to find the reason and give a message
like "It's probably because x". Not sure what algorithm we'd have to use but
I'm interested now.

