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.
> 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.
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.
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.
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.
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.
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?
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.
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?
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.
> in non-polarized light, the "amplitude" of the light wave points in all directions
The average is all directions. Each individual photon has just one direction. But photons are not like regular objects, if you send polarized light through a polarizer that is tilted 45 degrees relative to them you don't block the light entirely like you would expect, instead half the light gets through. I guess you could interpret this as each photon having a 50/50 chance of making it though.
> The amplitude of a light wave doesn't literally mean something is oscillating up and down, right??
Yes, it does mean that. The "something" is an electric and magnetic field. Does that count as a something?
Remember that a moving electric field induces magnetism, and a moving magnet induces an electric field. So the two fields essentially induce each other, that's why light can never stop moving, or even change speed - the fields would no longer induce anything.
> The amplitude is just the light's intensity.
No. The amplitude never changes. Intensity is the number of photons. A single photon doesn't really have an amplitude that way you would think.
I actually had the same misconception about light when studying it in highschool. I though that the up/down things that the teacher was drawing on the board was not literally how it worked (transverse wave) but that it was a measurement of the longitudinal wave. I think because I knew how sound worked, and I was thinking that way.
It turns out that it actually is a transverse wave in the electric field with another transverse wave in the magnetic field offset by 90 degrees. There is a good diagram of how it 'looks' here:
No, it's not a transverse wave in the sense that you're describing, like a wave in water. It's a wave in the E&M fields, both of which are 'vector fields'. Mathematically, we describe both electric and magnetic fields as a vector (a direction + length, like a little arrow) at each point in space. Light waves are oscillations in the lengths+directions of these vectors. There's no medium moving transversely, but the vector field points in the direction and with the magnitude drawn in those squiggly line diagrams.
See Maxwell's equations, which describe how those vector fields change over time. They do not describe how any sort of medium moves over time.
Yeah, you're right. I don't mean transverse in that it is a wave in water. There is no 'water' particles there to be moving up/down left/right.
Interestingly, Maxwell himself worked in a time when the aether model was dominant; that there had to be something for the waves to be moving in/through. His equations held up under both the aether model and special relativity which made aether unnecessary.
There's always going to be a limit to how well any macroscopic analogy can possibly describe what's going on with photons and light, but some metaphors work better than others. the trouble with the 'light is a particle and a wave' meme is that people try to combine two mental images - a cannonball flying through the air, and n ocean wave moving up and down, or a sound wave moving back and forth, and get a completely weird mental image of a cannonball flying along a sinewave path, or speeding up and slowing down. This isn't helpful.
Instead, you need to extend the metaphor in a different direction. Let's keep photons as cannonballs flying in straight lines. But now, imagine the cannonballs are constantly spinning. Some are spinning fast - they have a lot of rotational energy - they rotate with a high frequency. Others are spinning more slowly - low frequency, low energy cannonballs.
Now, which way are they spinning? Some have topspin or backspin, meaning they have a horizontal spin axis; some have sidespin - their axis of spin is vertical. Others might be spinning in a spiral - as if the barrel they came out of was rifled - so their axis of spin is aligned with the axis they're flying along.
You can imagine lots of cannonballs all flying along the same path, at the same speed, but they can all have different spin frequencies, and be spinning around different axes. Amplitude means more cannonballs. Higher frequency means more cannonballs spinning faster. Polarization means all the cannonballs are spinning round the same axis. Coherence (like in a laser) means all the cannonballs are spinning at the same speed and are pointing the same way as they pass the same point.
This maybe works better as a way to layer on the additional attributes a photon has - a frequency and a polarization - than to try to imagine some sort of transverse wave pattern. It also helps you deal with the idea of 'how do different photons carry different amounts of energy?'.
But, this is just a metaphor. Photons aren't really spinning cannonballs. It doesn't explain why thin slits cause polarization (and gives you a probably somewhat intuitive but definitely very wrong explanation for why bouncing photons off a surface causes polarization, so be careful.). It won't get you one jot closer to understanding quantum mechanics (no classical metaphor can do that), but it might just help you visualize how light can have mixtures of frequencies, polarizations, and amplitude, while still being just a bunch of particles.
What you're probably hearing is probability amplitude, which is the product of a wave function with its complex conjugate, rather than amplitude referring to wave intensity.
If you're interested in this stuff, check out the 160 or so videos from leonard susskind on youtube on modern physics.
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.
I'm having a hard time finding the orientation of my phone. I can see yellow artifacts but they're not coherent like on other LCDs. And when I look through polarized sunglasses there's no blocked angle. It must be using some alternative polarization even though it's a regular TFT screen.
There's certainly a value in not having your phone screen dimmed by sunglasses.
Wait I think I do.. Can't say for sure but they look like two small yellow marbles stacked vertically. What can I say about the polarization of my lcd?
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.
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.
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.
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!
>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.
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.
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.
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.
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.
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.
Article: http://news.discovery.com/earth/navigating-by-sunstone-and-a...
Paper: http://rspa.royalsocietypublishing.org/content/468/2139/671