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If you've been watching SciShow for a while, and you're super dedicated and I appreciate that if you are,
如果你关注《科学秀》的话，
the title of this video might look a little familiar.
你或许会觉得本期视频标题有些眼熟。
That's because a few years ago, we made a video on polarized lenses and how they reduce glare.
那是因为几年前，我们做了一期关于偏光镜片以及它们如何减少眩光的节目。
But thanks to some comments from viewers, we recently realized that we mixed some things up in that video,
但是感谢一些留言者的评论，我们最近发现在那期视频中，我们将一些概念混淆了，
and we wanted to set the record straight. So here's how polarized lenses actually reduce glare, and where were wrong!
而且我们希望在此纠正一下。因此有了以下内容—偏光镜如何真正减少眩光。
Light travels as something called a transverse wave, where the direction it waves is perpendicular to the direction it moves.
光的传播被称为横波，横波中的波长方向与其移动方向是垂直的。
It's like how water waves — which are also transverse until they reach shore — move across the water:
就像是水波—其在到岸之前也是横向的—横跨过水面一样：
the wave moves forward across the surface, but the water itself just bobs up and down.
波长向前移动跨过表面，但是水本身在水面上忽沉忽浮。
Similarly, light waves can oscillate up-down, or left-right, or any diagonal in between as they move forward through space.
同样地，光波可以上下振动或是左右振动，或是在移动来回的对角线之间振动。
And the direction light oscillates is called its polarization.
光振动的方向被称为偏振。
Now, just as we English-speakers say that the direction between north and east is a combination of the two -- in other words, "northeast"
现在，我们说英语的人称东北之间的方向为“东北”
physicists think about all polarizations as a combination of just two key ones.
物理学家将所有偏振认为是两个关键点的结合。
There's vertical polarization, which oscillates up and down as the light moves forward,
垂直偏振，当光向前移动时，垂直偏振上下振动；
and horizontal polarization, which oscillates left-right as it moves forward.
水平偏振，光向前移动时，水平偏振左右振动。
And just like northeast is a combination of north and east, any diagonal oscillations are just a combination of horizontal and vertical.
东北是东边和北边的结合，任何对角振动都是水平和垂直振动的结合。
Light from something like the Sun starts unpolarized, meaning it's oscillating in random directions.
从太阳等地方照下来的光开始都是非偏振的，这意味着其振动方向是随机的。
Some light is fully horizontally polarized, some is fully vertical, most is all sorts of combinations of the two.
一些光完全是水平偏振的，一些是完全垂直偏振的，多数光都是两者的结合。
Okay, so far, so good. That's it for the vocab words, and we had most of this in the last video.
到目前为止一切还不错。这是词汇单词部分，上个视频中我们讲了很多。
But here's where we get to the explanation of how polarized sunglasses work and where we went awry.
但是我们要接下来要解释偏光太阳镜的工作原理以及我们上次视频出错的地方。
We said that unpolarized light reflecting off a horizontal surface, like a lake, all gets polarized in the same direction.
我们之前说反射水平面的非偏振光，比如湖面，都会在同一方向变成偏振光。
And that isn't quite true; unless unpolarized light hits a perfectly flat surface at exactly the right angle,
这么说是不对的，除非非偏振光打在非常平滑的表面，且角度没有任何误差，
some horizontally polarized light gets reflected and some vertically polarized light gets reflected.
否则一些水平偏振光会被折射，一些垂直偏振光会被折射。
The closer you are to that perfect angle, the closer you get to reflecting only light that's polarized in a certain direction.
你距离完美角度越精准，你所折射的就越有可能是某种角度的偏振光。
The bigger problem was that we said light reflected off a horizontal surface is vertically polarized — that it oscillates up and down.
更大的一个问题是我们之前说反射水平表面的光是垂直偏振—即上下振动。
When actually, it's the exact opposite of that. Light reflected off something horizontal tends to get horizontally polarized.
真实情况正好相反。反射水平表面的光可能得到水平偏振。
It oscillates side-to-side, parallel to the surface it reflected off. So the glare off a lake or road is mostly horizontally polarized light.
边对边振动，和其反射的表面相平衡。因此湖面或道路上的眩光多数为水平偏振光。
And this is where polarized lenses come in. They tend to be coated with long, thin molecules lined up in horizontal rows across the lenses.
因此就有了偏光镜片。它们表面覆盖有长长的薄分子，排成水平的一行穿过镜片。
These long molecules can only absorb light that oscillates along the molecule,
这些长分子可以只吸收沿着分子振动的光，
so the rows of horizontal molecules absorb horizontally polarized light before it gets through to your eyes.
因此，水平分子行会在水平偏振穿过你的眼睛前，将其吸收。
But they let vertically polarized light right through.
但是它们会让垂直偏光正好穿过。
So, polarized sunglasses will almost entirely block glare from horizontal surfaces since it's mostly made up of horizontally polarized light.
因此，偏光太阳镜几乎完全阻挡住了来自水平表面的眩光，因为偏光太阳镜多数由水平偏光组成。
They also block the horizontally polarized part of sunlight, and since sunlight is unpolarized,
它们还会阻挡阳光中的水平偏振，由于阳光是非偏振的，
that means some light can get through, but not all of it.
这意味着一些光可以通过镜片，但并非所有。
If you turn the lenses on their side, suddenly the horizontally polarized light isn't in the same direction as those molecules any more,
如果你转动镜片方向，突然，水平偏光就和那些分子再也不是同一个方向了，
and you can watch the glare come back. And, in the last video, we got that backwards as well.
并且你可以看到眩光折回来。上期视频中，我们试了一下。
Since we were saying that glare was vertically polarized,
我们之前说眩光是垂直偏振，
we said that horizontal molecules absorb vertically polarized light, which is not the case.
水平分子吸收垂直偏光也是不对的。
What is true is that polarized lenses tend to work best fairly early and fairly late in the day,
事实上，偏光镜片在一天的晚些时候效果最好，
when the Sun is close to that critical angle where just about all its reflected light is horizontally polarized.
那时太阳距离临界角很近，在这个角度上，其反射的光都是水平偏振的。
Either way, their ability to block glare without making everything super dark makes polarized sunglasses pretty useful.
无论哪种方法都能阻挡眩光，又不会让你的视角变得黯淡，所以偏光太阳镜还是很有用的。
But it's definitely the horizontally polarized light that's getting blocked. Thanks for watching this episode of SciShow!
但是它们所阻挡的绝对是水平偏振光。感谢收看本期《科学秀》！
We fact-check all our videos, and we work really hard to do that,
我们会努力查核所有视频，
but we appreciate you all letting us know that this one slipped through the cracks.
但是我们也很感谢那些提醒我们视频有误的观众。
If you're interested in learning more about the physics of light,
如果你想学习更多关于光的物理学，
you might want to check out our video about sonoluminescence, where sound creates light.
你或许会喜欢那期关于声致发光的视频。
