WEBVTT
Kind: captions
Language: en

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I'm in Tromsø in Norway,

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That is the Tromsø bridge,

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and the beautiful Arctic Church there.

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Now, if you've been following my videos from here for the last couple of days,

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you might have noticed something a bit weird

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every time I'm under artificial light.

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And let's be honest: That's most of the time.

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Because, while it does get light in the middle of the day here,

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we're in the Arctic Circle,

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it's winter.

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The sun doesn't get above the horizon.

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Mind you, when it does get light, this place is beautiful.

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Anyway, you might have seen a bit of a weird effect,

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if I take a slow motion video of that streetlamp, and the ground under it,

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you'll see what I mean.

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There's this kind of weird strobing, rolling effect going on.

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And the reason for that,

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is something you might not know,

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the difference between the European and American power grids.

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See, the European power grid runs at 50 hertz,

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50 cycles a second.

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That means the alternating current in the wires

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switches direction,

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a hundred times a second, 50 cycles

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back and forth, back and forth

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And that means all these lights, that you can see,

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pretty much, dim imperceptibly

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a hundred times a second.

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Not enough that you can see it with the naked eye,

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but the camera will pick it up.

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Now, okay, that's not a major problem

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if your camera runs at the same rate as the lights

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The lights run at 50 hertz,

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British television runs at 50 hertz.

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But unfortunately, I'm using an iPhone,

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which is designed in the U.S.,

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for the American power grid.

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The American power grid chose to run at 60 hertz,

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60 cycles a second,

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so American TV runs at 60,

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or 30 frames a second.

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So, the camera is recording at 30 frames a second,

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the light is pulsing at 50 hertz,

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those two are out of sync,

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and so sometimes you get light, and sometimes you get dark.

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But, why the rolling effect?

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Well for that,

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we have to understand the rolling shutter in a camera.

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Or in any modern camera.

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Old film cameras don't do this,

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obviously, they just expose a shot

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every time a frame goes by.

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But, no-no, not this.

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THIS camera, and all modern cameras

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run, a line at a time, scrolling down the screen.

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Which means it can take a fraction of a second difference

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for it to go from the top of the frame, to the bottom

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And the result is this rolling effect.

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Some of those lines are recorded when the light is fully on,

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and some of those lines are recorded when the light is dim.

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And that's the reason.

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That's the reason you have this kind of weird, artificial,

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rolling light problem,

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when you're filming with an American device in Europe.

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'Course the easy way to fix it,

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would be for Apple just to have a 25 frames a second option,

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but that would be far, far too difficult for them...

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And THAT is something you might not have known.

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